And there's that.
Unless it's a deal where the P12 network is dying for content. I suppose that *could* be the case. In a 16 team league, it's more likely that you'll have 4-5 teams that don't get picked up by the national networks on any given Saturday. In those cases, the P12 network would be able to show additional games and generate additional revenues no matter who gets added to the league. I realize that's a lame reason to expand, but there you go.
Would a live CSU game generate enough ratings and add revenue over a USC replay to justify paying a conference share? I don't think they get close. If you need content you put some college girls in tight shorts and show intercollegiate beach volleyball. Most of the country would have more interest in that than seeing CSU play Oregon State in football.