The rhetoric from the talking heads is that TCU has a chip on their shoulders and they wanted to show the committee that they made a mistake in not putting TCU in the top 4. I guess that's good motivational fodder for the team, but realistically it's the fault of the Big 12 conference leadership as much as anyone.
They decided that they would try to manipulate the system and ignore their own bylaws to get at least one team (hopefully both) into the playoff. The committee was right in what they did IMO. They set an example for the future and let everyone know that they're not going to go for bullshit like that again. I think that TCU would have been deserving of a spot, but they can thank their own conference for fucking them out of the opportunity.