The Henson family was also on board with his firing so my guess was he was difficult to work with and eventually Disney/Henson family got tired of it. Disney could have handled it better, but I don't think he was a walk in the park either. For Disney and The Hensons to comment on this publicly makes me think they really have a case, so to speak, against what he is saying in the press. They usually keep all this kind of stuff in house.