Quite simple.
Wow killed all other MMORPGs...
And now people are realizing that WoW is actually a pile of boring, repetitive crap which offers 0 challenge unless at the absolute highest level of play, and even then, only for about one week before the top guild finishes the content that was released with the new patch.
I played EQ, Shadow of Luclin, Vex Thal existed and was available, including all mobs, from the get go... But it took FoH AGES to actually play through the whole content and actually key up, get in there, and several more weeks to actually figure the encounters and beat them.
Even party content was not easy, if you were not geared... And gearing was much more difficult than it ever was in WoW (I laugh my ass off when people saying WoW classic is "hard"...). And if you messed up by unmezzing a mob, you'd die quite quickly anyway. It required more skill and coordination as a team in a day where voice communication was bad or nonexistent compared to today.
Yes, sure, the new "bosses" and "mechanics" and gimmicks are more numerous than and more varied than they were in EQ... But I have never felt the same thrill as being rezzed by a rogue in a deep corridor of Vex Thal and having to coth people one by one as the rogue used all his defensive disciplines to keep the wandering mobs up until there were enough people to fight.