You may be right about CU, but my guess is that you are not. It may be that the only school in the current Big 12 that would have been more inviting to the Pac 12 than CU is UT. Academics is very important to the Pac 12 and CU has big, big bucks and clout in its research. Undergraduate rankings have CU in the upper middle of the pack, but as a research institution it consistently ranks very high. And it is the research end of academia that interests the other institutions in a conference. Athletically, CU football still has a viable brand, despite its recent lack of success. If the program turns around, as it always has in the past after dry spells, it will be a valuable commodity for the conference. Its basketball program, surprisingly, is now one of the strongest in the Pac 12, so they can't be too disappointed there. Finally, I am sure the conference is very happy about the geographics of Colorado. They must love the constantly growing Denver market. I know from a conversation I had with Larry Scott, the commish, at a fundraiser last Fall that having Boulder and Colorado be a destination for the other teams and fans in the conference was vitally important in the conference's decision. He also told me the conference never stopped wanting CU after CU turned them down in the 1990's to stay in the Big 8/12.
Other than UT, I just don't see anyone else in the current Big 12 that would be more inviting to the Pac 12, which is a different breed of animal than the other major conferences in what it finds important beyond the money (which of course is a primary concern of all conferences). OU has the great football program, but it strikes out in the academic and geographic aspects, as well as the TV market aspect. The other Texas schools are just UT satellites. Kansas schools don't bring any more athletically than does CU, other than KU hoops, and socially and academically are less appealing to the Pac 12. TCU and West Virginia obviously are not Pac 12 fits in any of the categories.
I think the Pac 12 knows that, other than UT, CU was about the best the Pac 12 was going to get from west of the Missouri River, and I don't think they would ever want to expand east of that. I imagine they are happy they got CU.
Now, Utah on the other hand ...