I can add a little to this, there are some legal issues for NBC to consider that have nothing to do with any racist comments. I work in broadcasting, and there is a law that requires broadcasters to offer equal and/or fair time to candidates. This doesn't apply to say, news coverage. But if you sell a commercial to one candidate at "x" price and his opponent wants to buy the same amount of ad space, you are required to sell that time at "x."
Now say a host or contributor who is on the air on your station runs for office. Some district courts could see that as "free air time" even if the election isn't even talked about or mentioned. Meaning you may have to offer free time to all opponents. And ad revenue from an election cycle is super lucrative. The communications company I work for doesn't take chances with the legality. My company took a contributor to one of our programs off the air when he ran for public office. Actually we had legal draw up a document he (our contributor) signed agreeing not to talk politics or the election on the air, and we took it to his opponent asking him to sign it and waive his appearance on that show only from the legal requirement. And the opponent refused to do so, preferring that we just take him off the air.
Now that was at a local level. NBC could more easily than my company fight a decision against them, and as a national broadcaster different rules apply. However NBC may have figured, as did the company I work for, that a simple solution is better in the long run than a long and drawn out legal battle.