My bet is that he really does have some sort of personal, long term issue going on. My bet is on health.
Despite what others may think, he really was successful compared to the alternatives that were available to MSNBC to put in place of him.
When Rachael Maddow is beating you in the ratings, your health is going to suffer, no matter who you are.
He got canned because no one was watching. He became predictable, boring, vitriolic, and repetitive.
Its all about money, and Keith isn't a draw anymore.