It's a psychological issue IMO. USO 2011 he lost first two sets by being passive, then won next two by being extra aggressive. Then he got himself into a hole again by being passive and waiting for mistakes. Finally he escaped with that crazy return winner and some Federer's mistakes. If he was burned more times for being passive, maybe he'd play differently, but he's won 16 GS and fukton of titles so... I think he doesn't have ultimate confidence in his attacking game, which is sad, because it's a very good one. Also, when he falls on defensive game alone, his variety gets minimal and that hurts him. Personally, I believe that not being supported by crowd in most places makes him even more defensive. Like in football, playing away teams always play more defensively than at home where they are invigorated by the crowd.