The general vibe I get is that which ever fan base feels like they have the upper-hand is less interested in playing the game. If everyone already thinks you are better than your rival, why play and risk it?

Utah had no interest in playing BYU until Utah lost 3 games. Right now, it is a close call. But I get the impression some Utah fans would like to play the game to put BYU in its place, so to speak. Others are satisfied that BYU doesn't have a legitimate claim to superiority and are fine not playing the game.