Pride? The in-state bragging rights?
What of real value does BYU gain?
Well, as long as the "Holy War" was an annual contest, they gained the playing of one of the most intense rivalries in college football. That's no mean thing.
But now Utah has done away with that. BYU plays Utah only at Utah's convenience.
Guess what? Utah adds little of value to BYU's schedule that we cannot replace. On the contrary, playing elsewhere adds a great deal of value that Utah cannot possibly touch. Utah is a mid- to lower-tier PAC-12 team. There are any number of games that would be equally or much more prestigious, and that would give BYU exposure beyond the state of Utah.
Now, if we were playing Utah in November, it would be a harder decision. But, unsurprisingly, Utah has already put a stop to November games with us. The Utah game has become a relatively unimportant game.
Stop playing Utah altogether, forever. Screw them.