Current was pretty stupid for hiring him to start with.
This wasn't like hiring Cenk Ugyar or whatever his name is. Cenk got fired because he didn't toe the party line, but he was professional. Olberman was a ball of ego, and they should have realized it early on, from the fact he's been fired from about three places previously.
Really, Olbermann's biggest problem was that he only got famous by being the voice of Bush Derangement Syndrome. When Bush went off to enjoy retirement, there was Olbie, still being mad at a guy who wasn't playing anymore...