He probably realized maybe he's really better off working somewhere else. Most people get bored of their same job after 5 years anyway. Maybe his team he worked with started to suck and he didn't want to be part of it. Who knows? He surely did much for this game. But now I am sure many will wonder how things will go from here. He left at a pretty bad time when the new expansion is being worked on heavily. Way to fuck over everyone.