Arizonas bring more collectively to the table competitively when considering basketball than Utah and CO. Utah is garbage in basketball, and CO is worse. CO has done nothing in football in 20 years, despite the hype around Sanders.
Plus, the Big 12 already has the SLC market. The Phoenix market and the command that the Arizonas have on it is more impactful than the Denver market and the lack of influence of the Buffs there.