Actually I did stop playing wow to play d3. for like 3 or 4 weeks.
really though, it's just... it's just time. the game is a fantastic game, one of the best ever made, but it's been the same thing with new coats of paint for almost a decade now. you can only do this same dance so many times before you sit up, ask yourself "what else is there", and wander off.
I was in a world top 80 guild in vanilla. I personally was the highest DPS on the server for a good while. It was a 7-day-a-week job, but I was young and my GF (now wife) raided with me so it was doable. we both burnt out about the same time the rest of the guild did, it colapsed in on itself about the time we realized that the imminent expansion would completely negate everything we'd done. and it did. complete burnout. left the game for 6 months at least.
raided with a semi-serious raiding guild in TBC. I fought my way back up into a server-best guild again by the end of the next expansion (wrath is still the best thing they ever made imo), just in time for it to all repeat again.
didn't bother raiding cata. same song and dance again.
haven't even SEEN most of mop, i mostly just level alts now. dungeon finder circa level 15 to 55, and questing in northrend and cataclysm for nostalgic purposes, that's all the game is to me anymore, a time sink for nostalgic purposes. like putting weekend at bernies on the tv while you're cleaning the house.