Well, judging from personal experiences:
The guild I spent my whole Legion in, raiding, pvping etc. Disbanded not long into BFA because people grew bored too fast.
I found a new guild, and cleared HC Uldir + some Mythic bosses, then that guild disbanded aswell, because people quite because of nothing to really do, except farm m+ and hope for the right Azerite in your weekly cache.
So I stopped raiding, and started PvPing, got to 2k rating, had a ton of fun, got some new friends etc. Then all my friends who I have played this game with since between Vanilla and Cataclysm quit one by one. I see them log in every now and then, just to log out.
And a week ago I my self quit, for the first time since 2004 I actually unsubbed to the game. I've been through pretty much everything this game has trown at me, and I've sucked it up, gone play something else while there was content droughts etc. But never have I actually unsubbed to it, as the money have never really been a problem.
So judging fromt he fact that TWO rather big raiding guilds disbanded before the first tier was even done, they didn't even bother with Mythic, which most HC guilds do. And all my long time friends quit one by one. Ye, BFA was one huge mistake.
Will resub next patch and check it out for sure, this game is in my blood and have always been. But at the moment it just feels.. off.