The stated goals of BYU football independence are and have been: exposure and fan access.
If BYU plays in the MWC, our exposure and fan access take a major hit.
The expanded AAC (+Boise & SDSU) would give BYU football exposure (ESPN TV deal, national conference, rankings opportunities, etc.) and fan access (national conference, with games from California to Texas to Florida to Pennsylvania), along with legit access to the expanded playoff.