I see this all the time when new games release -- attacks, slander, and "I'm leaving <fill in the blank> for <fill in the blank>." Why? Why can't you play more than one? Why can't you enjoy multiple games?
Personally, I play WoW, LotRO, GW2 and PS2 (which I guess is more of a shooter than an MMO). This isn't even counting the SMITE, Diablo, Hearthstone, and single-player games in my library.
WoW is my raiding, hang-out-with-friends, heavily invested in the lore game.
LotRO is my RP, play music, and explore Middle-earth game.
GW2 is my fast paced, jumping puzzle, change-of-pace game.
PS2 is my shoot people in the face with a rocket launcher game.
I find that by having a nice spread of various titles, there is no burnout or boredom. If I don't feel like playing something for a few days, I don't play it. There are too many fantastic titles on the market to limit yourself to just one.