Probably just burned out from chess, especially training the whole day for competitions.
We are animals and eventually the brain will rebel against extreme repetitive mental effort that is perceived to be at least partially useless (and given he's already been the world champion, it's easy for part of him to think there's no point in training).
We are animals and eventually the brain will rebel against extreme repetitive mental effort that is perceived to be at least partially useless (and given he's already been the world champion, it's easy for part of him to think there's no point in training).