Athletic conferences pretend like that counts, but it doesn't. The calculation is simple: does adding BYU mean more money for everyone? It doesn't.
You can argue they took Utah over BYU for cultural reasons. That may be true, but you can also rest assured if they thought taking BYU meant more money for them then Utah they would have done that. They got to negotiate deals based on having the SLC market either way. Adding BYU doesn't add a new market to negotiate more TV money so why bother? It ain't about competition, education, or culture. It's about money.