Because they’ve overplayed their hand on RNG. Blizzard has been for years now, trying to figure out how to keep us enticed in content long enough to push out new content.
The question is why have they layered it in 10 layers of RNG to do so? What’s different about obtaining raiding gear now than it was back in WotLK?
For starters, they’ve added personal loot. We also have re-roll tokens for additional chance at loot on any boss we want. Master loot is gone as far as I know, or at least personal loot has completely overtaken it. M+ provides us with similar or equal loot for raids.
They’ve increased the amount of ways we can obtain loot, but are we getting loot faster or slower?
Even with personal loot, the chances of getting gear from a boss are probably 100%. Not for individual people obviously. I’m not sure how the system works, but I haven’t been in a raid where 0 people got loot from a boss. So do we all share chances of getting loot from a boss? Or are we competing in chances for loot against each other?
Even though its called personal loot, I don’t think everyone in a raid group can get so lucky as for everyone in the raid to get a piece of gear, there’s probably a limit on how many pieces can drop from a single boss. In a way, master loot might as well still exist, the difference being you can’t ninja loot personal loot.
At least with M+ we have guaranteed loot at the beginning of each week, so technically gearing up is faster, just not BIS. Assuming of course you can get into a group to do M+'s high enough to push your gear.
The new M+ loot system will definitely increase that speed even more by offering us a choice among random pieces of loot, even if its not the pieces we want, if its an upgrade, and the option is there you can pick it, instead of waiting for the RNG gods to pick you.
I think the idea of personal loot is more of an illusion, but also a protection against greedy people. Same amount of loot drops from a boss, you just don’t get to decide who receives it, unless it not an upgrade and you can trade it to someone else.