He's a good playcaller but trying to do everything and still be the head coach was too much for him.
Well that, and behaving like an adult. lol
Agree that trying to call the plays and be head coach was too much. I remember that Carroll tried the same thing with the defense and figured out pretty quickly that it was too much. Kiffin kept stubbornly insisting on keeping the playcalling duties himself, even after it was painfully obvious that it was too much.