No other non-P5 candidate can bring a game to the conference inventory every other year of similar rivalry caliber.
CSU can bring the Colorado rivalry, which likely elevates somewhat in stature with a CSU call-up - but that's it.
Cincy doesn't play Ohio St. at home or Indiana or Louisville or anyone other than Miami (OH) consistently OOC. UConn has 4-game deals with Boston College and UMass, where UConn plays one OR the other in most years over the next decade. Memphis plays Ole Miss twice in 4 years. Houston plays Rice a lot.
Everyone focuses on markets when they discuss expansion. But Oklahoma St.-Baylor was among the top-rated Big 12 games last year. It's not because of the powerful markets of Waco and Stillwater, it's because casual fans in Dallas, Houston, Atlanta, Phoenix, and Michigan tune in to that game.
BYU-Utah and CSU-Colorado have the potential to be the type of games that can get casual fans nationwide to notice and tune in. That = ratings and $$.