They aren't scared to play each other. They want monster games that people want to see every week. With an expanded playoff you are getting in the 12 team playoff at 8-4 in the new SEC.
Except with a 24-32 team league they won't be monster games nationally, they will be monster to the fans of teams in the league and no one else.
The success of an NFL-lite league is completely dependent on a good chunk of fans of the other 30-40 P5 conferences adopting one of these teams that's in the club. That's not going to happen. I'm not sure of the time frame, but ultimately that model will NOT be lucrative.
Right now these games are huge because:
A. there is still SOME level of passive viewership, though with so many options, more migration from network TV that becomes less and less all the time. So you simply can't count on this at all moving forward.
B. There are fans of the 60ish teams in P5 conference that have a connection in some way. When that is gone those viewers won't watch, and they sure as hell won't go out of their way to watch/subscribe, which is the way it's moving. The idea that fans of teams that have almost no chance of a playoff or national title don't matter is idiotic and so clearly false.
C. Pretty much every college FB fan is an NFL fan, but the opposite is most certainly not true. Fans of teams that get left out aren't going to decide to jump on the bandwagon of a team in NFL-lite. They'll just keep watching the NFL. They can't look at the league, see that they've got all the regions covered and think it's going to work. "well, we've got Michigan and OSU, so the great lakes region is covered." No, Wisconsin, Minn, Indiana, Purdue, etc. fans will just be strictly Packers, Vikings and Colts fans. They aren't going to start rooting for Michigan an Ohio State, and if their school has no tie, they aren't going to watch.
I think a P5 type breakaway with about 60 teams would be the optimum for keeping college football a big money maker.