The PAC wanted a championship game. They petitioned the NCAA to have one with just 10 teams. Over and over for several years they were told no. They explored their options, BYU was a non-starter for political reasons, so they settled for Utah once Colorado came onboard.
Then Texas flirted and Utah went to the back burner. Texas did their Texas thing and eventually declined. The PAC petitioned one more time to do it without Utah. They were told no. With all other options exhausted, the PAC invited Utah.