Part of the reason there is that most people can’t put their finger on what, exactly, the problem is. And the few that can will often disagree.
I think the problem with WoW’s story is that Blizzard has deviated from the central theme of WoW, which is having a Horde experience and an Alliance experience.
For vanilla/BC/Wrath, you had different versions of most parts of the game, from leveling quests through dungeons (Halls of Reflection is a great example).
For the last 3 expansions, we’ve mostly had just 1 story, one-size-fits-all, for Horde and Alliance. So we’re getting half the story, and for a lot of people it doesn’t even feel relevant.
(And before somebody points at BfA, the primary story of BfA was about helping Magni. That’s what the primary focus was on, that was the climax of the expansion, and that’s what we were doing every day for 2 years - tending Azeroth’s woons.)
MoP was uniform in story. Horde players were even following Anduin around for an entire zone while leveling. The only difference was Wrathion lied to half the players.
WoD had separate stories… but they weren’t about the Horde and Alliance. So… meh?
Legion was 1 story. In fact the Horde was written out of the game for the entire expansion.
BfA had the Phony War that lasted less than a year and still wasn’t the principle focus of the expansion. Then it was back to Woons & Wrathion.
And in Shadowlands… in Shadowlands the factions aren’t there at all, which is a first. Even in Legion we had the Warden Towers world quests, but in Shadowlands? There’s nothing!
So I think Blizzard needs to get a Horde story team and have them make Horde stories and Horde quests, and an Alliance story team and have them make Alliance stories and Alliance quests. Because the further away from that we keep getting, the dumber the stories keep getting.