Everyone called it from day 1 of his breakdown. He would return and either continue Fez 2 and then spout stuff about how everyone is lucky that he even bothers to do this for them and that everyone should be thankful, or spout stuff about how everyone's not worth it and that's why he's not doing it.
But like dkamm said, it's just because he has no more ideas. He got way too confident because he had 1 successful game (I think it was pretty mediocre anyways) and announced a sequel to Fez way too quickly after the first one, causing him to get trapped into a corner, leading to his autistic breakdown. He's a total clown.