Yes. WoWs quality is just so big and they've had so many years and so much content to build upon. That and the movement in WoW is the best I've ever seen and played. Movement and animations are extremely important to me, which WoW succeeds at greatly.
Besides that, because I've played WoW for a relative long period (for me at least) everything has become repetitive. Thus, when I try playing a new MMO, heck even a singleplayer game, I can't stay focused because of how bored I get.