TL;DR - If you dont want to, dont read.
I am not that person who cites one reason for behavior, because all behavior can only change due to several reasons, as one thing has to be related to something else as to modify your perceptions and responses to something.
So, I am starting with personal reasons. Establishing “mental state”, not actually relevant to what I think of the game.
When I started playing WoW, back when it launched in Europe, I was living in Spain at that moment. I was in my mid 20s and I had a demanding work schedule which made me spend most of my time close to the computer, even if I had no work to do. Naturally I would spend the time I had to “wait” playing games or watching YouTube. I had less free time to play and lots of stresses to vent while playing, so I got hardcore raiding as ways to do something thrilling.
First major change in WoW for me was at the end of WotLK, 2010, when I was entering my 30s, moving to Asia, and changing my work schedule to a more relaxed one, thus able to travel more, spend more time away from computers, and at the same time, WoW was marching to cause the reasons I will list in the further on.
For all that, since Cataclysm, my WoW playing went from hardcore raider to “ok, lets raid”.
So now I move to lore.
For me, WotLK was the last expansion that had solid connections to the Warcraft RTS lore, and the last one trully derived from it. From Cataclysm on, if people pay close attention, the lore has been tied to somewhat real life popular events that call for external anchors, like Cataclysm tied to the hype of the 2010,2011,2012 predictions of the end of the World.
I was in Asia at the time of MoP and remember that despite all the “there were Pandas in WoW Universe”, the timing was clearly affected by the overall “China rise” and all the cultural curiosity people developed to Asian culture in general, the tourism here as going crazy, and every entertainment industry was betting on Asian themed everything.
2014 and Warlords of Draenor came with the climax of the tensions in Ukraine, the big rise of ISIS that would then only go down. War and Warlords were a theme everywhere.
2016 was a year plagued with fatalities from natural accidents, like the Earthquake in Italy, and all the instability regarding North Korea, China, and the intensification of “Global Warming Agenda”, coincided with the hype for Legion, for obvious reasons linked to the “great Satan”.
2018 was a very intense year on the rise of “left x right” political “drama”. People were more polarized than ever before, and ever after. In the “real” World, out of YouTube trash political commentary, real countries were struggling with this paradigm and culminated in the turmoil that was the political arena for “leftists” and “rightists” all over the World. No better year would be for launching Battle for Azeroth since the Cuba Missil crises.
Of course, since then, Warcraft lore has been tied to the idea of western politics, bipartism and capitalism vs communism. There is a cover of fantasy lovecraftian lore over it, but reading those works one can realize they were changed essentially, from a “all is lost and nothing matters” to “when all is lost you gotta stick to the principles that got you lost in the first place” kind of thinking. The so called “grey morals” of Illidan and the “Shadow” are just grey in appearance, because looking inside, it becomes a very determined field of black and white squares, too little for the more distracted to notice. There is no balance, you just change that light and shadow are not the opposites anymore, something else is. Pretty much the same as using “criminals” to fight “worse criminals”. Still good and evil, but in a disguise.
That is what brings me for the change in BfA to Alliance, after the first 5 years of Horde only play and other 5 years of “lets make an alliance character and see what this fuzz is all about”.
After WotLK, the Horde would never be the same again. All that made the Horde whole, the Honor based coalition inspired by the societies in which there are no supreme leaders and instead a council of chiefs decide what the warchief enforce, the Horde became what I like to call “a plot device to advance alliance storytelling”. The blatant exposition of that came in BfA when clearly, the lore was sold as a “Hordecentric” content, when it was, like many times more subtly done before, using the Horde to test waters for Alliance storytelling, like a “focus group” for Alliance more well rounded version. Every time, since WotLK, the Horde player is compelled to act out of character, and for the detriment of the Horde as a whole, undermine its cohesion, its values, and its lore, in order to create a situation in which Alliance leaders end up coming to save the day and moral grandstand the Horde. This calls for the tale of “democracy is good, freedom is good, anything else is bad” kind of thought, but executed as a straw man to prove it right. The horde is that straw man now.
I have no problems with story I would not do myself, but what I really dread is cooked up stories that a player has to act outside what would be logical and coherent, to suit narrative needs. So that is why I definitely changed to Alliance in BfA, as Horde is not fun to play for lore reasons, the only reason choosing a faction really matters to me.
That brings me to Gameplay.
I will never say gameplay in vanilla was good, because it wasn’t. Not even “compared” to anything at that time. Vanilla WoW was ONLY and MOSTLY played for Warcraft RTS fans, their friends and people curious about it. It was buggy, it was slow, it was unbalanced and it was too little for all the people trying to play it.
TBC was the first and only expansion in the history of WoW that solved more problem than it caused. But it was the first expansion and the first expansion to bring the problem that would only get worse in WoW - consistency.
From TBC on, WoW marched to the new-player-centric-no-alts approach. The game started with the now not so subtle time gating of content. Instead of allowing people to reap the rewards of dedicating more time to play and having played the longest, the game started its slow descent into the idea that people who play the game from earlier, and for longer sessions, have to be stopped to avoid being too distant from new players. That might seem a legit concern due to perceived harsh environment to a new player, but this environment is WoW own making, when it promotes not only factional competition, but in-faction competition. Contrary to the idea conveyed, you will compete with other players from your own faction for resources and powers, creating the notion that if a player is newer or less skilled, you have no advantage in helping them, and all the advantages in keeping them from getting better and experienced. This notion created the need for such mechanisms as time gating, class normalization and racial normalization.
WotLK was the last expansion that all those were subtle. Since then, the game is being clearly modeled to suit the idea that anyone can start playing today and outdo experienced players in a matter of days, if passing through a money gate, and in a matter of weeks if passing through time gate. The better and the more time you spend playing is actually punitive, because after the “critical time” of progress, time gates will kick in, and the more you play past that point, the more time you are wasting.
From Cataclysm, WoW started to apply what will forever by known as the “WoW paradigm of You are having fun wrong”.
It was nothing new, but WoW devs were the first to after a while say textually that their game is changed in order to get people to “have fun correctly”. The moral child of Blizzard, Anet, said it more candidly, but it was after WoW devs made it “a thing”.
They would punish players that came up with new and inventive ways of gameplay, making from subtle “invisible walls” to blatant “one shot mechanics”, to avoid players from doing bosses, quests and instances in a different way than it was designed to be. If you doubt it, just do a quick search for ‘Warcraft having fun wrong’, and all the enlightenment on the subject will be shown.
In WoD that reached a level that I would never more try to do my best, as I noticed there wasn’t any more advantage to play the expansion for me than it was for anyone joining the game in the inter expansion periods. I could play the lore of each expansion and stop playing, because if I came back in the last patch of one expansion, I would be gifted with gear and experience to play the next lore as if I was playing all that time I spent away. So, why bother ?
And that leaves the last one: Why changing from a multi account limit alts to single character ?
Part of it is made to avoid “player envy”, the sense of injustice one have over something that does not affect that one. It was the idea that people who can play multiple accounts and handle alts are doing something unjust. From the point of view of multiboxing, the line in “rules” is clear: You can multibox as much as you want provided that one click for account is directed to one action only. Which means you can use one click to do one action in each account, but you cant “autoplay” as in one click makes multiple actions for one single account or for each account, ie, multiboxing or not. That makes the idea that a player controlling 2 accounts and two players controlling one account each are bound by the same speed of reaction limit, thus making controlling two accounts less effective than 2 coordinated people with one account each. That on paper is very interesting, but you are gated by the game in ways that using multiple accounts gets less and less effective, once content is centered in individual account drive. Many things are limited to be done by one instanced player alone, so you cant multibox at all.
As for Alts, despite ONE aspect being open to alts, namely, pathfinder, all other things in game are designed to favor having one character in your account. You cant have several important items shared to your Blizzard account as they could be. Handling multiple alts is made harder by intent due to the format the client assumes, and from WoD on, it is increasingly time innective to make alts and try new things. The time gate will multiply, the more alts you have, making it very time consuming and tedious.
And that is why I changed to a Alliance single character casual gameplay. It is all WoW deserves at this point, and not so much.