I think there are a bunch of reasons:
1. They’re afraid of being labeled racist.
2. They have a personal stake in Obama’s success.
3. They love power over Truth.
4. They have “normalcy bias”, meaning that they think all of what’s going on is really just normal politics, because the alternative is just too scary for them to face.
I’m sure there are other reasons.
Those 4 certainly cover a lot of it (especially #4). Another reason is that it is very hard to "prove" what is going on in someone else's mind. It takes a lot of evidence viewed in context for a case to be made, and it certainly can't be done in these few minute segments on TV. That is why I think these types of segments do more harm than good. JMO.
5. Because they get paid for their oh so thoughtful opinion so they pretend to have given great thought to their opinion unlike the partisan hacks.
BTW, if they were paid for what their opinion is actually worth they would starve.