Main issue is competition, maybe not in MMO standards are increasing. People are playing other games that have recently released.
You have other issues like lack of "evolutions" of job designs from EW to now outside of further dumbing down of jobs and their identities with "reworks to job identity" promised next expansion instead of THIS expansion that people were clamouring for.
The gear grind is getting stale, especially with the "new" types of content to better bridge the gaps between roullettes and savage raiding coming out far too late in a raid tier instead of soon after or day one of the raid tier to add "variety" to the players.
Not making enough content for casual players while dumbing down the content you make for hardcore players because you are hoping those casual players will be "hardcores" at some point and don't ever do so because the prior point.
This has been a very weak expansion. I joined in HW and SB was my first current expansion I played through. That expansion people said was the worst one but... I can't say it was "bad". This expansion is just... unremarkable, far too tone deaf in the trying to be "safe" when they stuck with systems for 1 expansion too long.