MSNBC rode the left-wing thing to improved (still low, but improved) ratings, but there's a limit to how much Keith Olbermann or Chris Matthews one can take.
Besides, Tom Brokaw and Brian Williams appear to be openly revolting against appearing on the cable network, and everyone's at everyone else's throat, a condition that seems to follow Olbermann from network to network. The result: Olbermann and Matthews have been pulled from anchoring election coverage and debates.
Olbermann's weird "apology" for MSNBC airing the 9/11 tribute film at the Republican convention was the last straw; they're replacing him with David Gregory for debate duties. But they should have seen this coming the moment they hired Olbermann.