The Utes don't want to play BYU in the Las Vegas Bowl. It's as simple as that.
Referencing today's Trib article by J Drew:
http://www.sltrib.com/home/3231785-155/byu-football-hawaii-las-vegas-bowls
Per John Saccenti, the exec director of the bowl:
"Folks wanting a BYU-Utah matchup in Las Vegas shouldn't hold their breath, partly because Utah would have to lose to Colorado on Saturday to fall into that realm, and also because Utah played there last year.
Saccenti said there is "no-repeat language" in the bowl's contract with the Pac-12 to provide a team in the sixth-place range, but not necessarily a clause or actual rule. The language just allows the bowl, the Pac-12 and the school in question more options if any party feels the fit is not good.
"I have spoken to Utah. …. My sense is that Utah would not be as excited for that matchup as BYU would be," Saccenti said, also noting that Utah and BYU are playing next year (Sept. 10 at Utah) and that television viewers nationally might not be attracted to a "regionalized" game."
Should Utah lose to CU on Sat, they will do their best to avoid the Las Vegas Bowl matchup.
BYU wants Las Vegas, and in my estimation will probably get it. It is just time to expect a PAC12 opponent other than Utah.