I cannot see the B12 taking Colorado and UConn over Colorado and Arizona. We’ll end up left at the altar again. Seems appropriate for a CYO league member.
The University of Arizona sits in a more populated and faster growing state, has a larger enrollment and more living alumni. They're also in the AAU, which might appeal to some Big 12 university presidents. And adding a sitting Power Five school might be appealing to administrators concerned with "optics."
My personal view is that Big 12 making a long term decision based on the latter two would be stupid. I'd also argue that the former advantages are becoming less important while the relative importance of national brands is increasing.
On that front, Arizona football (like UConn football) isn't national brand. And the Wildcat basketball brand is good, but not nearly as strong as UConn. Bob Thompson (former FOX Sports president) rated Colorado and Arizona as two of the (four) least valuable schools in the PAC 12 for a reason.
UConn is a better long term addition than Arizona in my opinion.
(I have lived in Connecticut a few years now and my eldest daughter is an incoming UConn freshman so I should acknowledge that my views are perhaps less unbiased now than in the past.)