The ultimate reason is simple, and it's the same for all the candidates. Nobody available moves the needle.
Back before Jim Delaney ruined college football, the game was about regional rivalries and, well, fun. In that world, Houston was a natural fit in the Big 12 Conference. It was in its own version of the Big 12. The Southwest Conference was fun and surpassed only by the SEC in pure cheatin'. And that was only because Texas tattled on everyone.
If college football were about playing the game on the field, then Houston would be the obvious choice.