And Ore. They want to be careful going much deeper than that. Diluting the conference is a real concern. There was worry that adding UCF, Cincy and Houston was already doing that. Look how diluting the PAC with Utah and Colorado pushed out USC and UCLA.
If the BIG XII adds teams that are a net negative, like Utah was for the PAC, it will upset the already fragile stability.

Adding the two AZ schools makes sense. They are a stable package that adds a new region and helps geographically. They have been P5 long enough that they don't take away from the Conference. They seem like a decent cultural fit with the Big XII as well.

UW and Ore seem like long shots. They don't fit in with the culture of the Big XII. If they want in, the Big XII should accept them.
Ore st. Wash St should be on the table if it helps get Wash and Oregon to join

Utah and Colorado... What do they have to offer?
Colorado has the Denver market...maybe? A little success in the 90's?
Utah... Nothing... BYU absolutely owns the SLC market. Adding Utah and Colorado hurt the PAC more than they helped it. Adding them to the Big XII would likely have a similar negative effect.