The most obvious reason, which should be very simple to understand from fans of both schools, is that the U took a very measured and calculated action to marginalize BYU's football program. Anybody not willing to acknowledge this is a troll, or not very bright.
They knew BYU didn't have a conference, would have a tough time scheduling games, and decided to twist the knife.
The other reason is because Utah and Kyle are heavily invested in the game, and preparing for and playing the game took a lot out of Kyle and his team (not criticizing this, the Utes have the rivalry week prep and game mastered).
This is why i really hope Utah tanks the season and Kyle loses his job. I am also a petty person at times, though.