I say it's fear. It's not Beth. It's not money. It's not the Hamptoms. It's simply fear. His riddled with it. His fear grew out of when Hank died and Elliot Offen killed someone, and smashed the wall, and Cabby was talking to his TV and went to prison, Kenneth Kieth died in jail etc. It culminated with Artie's suicide attempt. The suicide attempt put the fear of God into him. He is paralyzed to do try and do anything funny anymore, including hiring a new comedian for the studio. Talking to himself and Robin parroting him and giggling like an idiot is the most he can cope with at the moment. He's ascared.