after reading this article:

https://247sports.com/college/utah/Article/The-Right-Fit-An-Oral-History-of-How-Utah-Joined-the-Pac-12-119713965/

A lot went right for Utah:

Getting Urban Meyer, winning the fiesta bowl, not losing Whittingham to BYU, if BYU tried to hire Whittingham one year earlier, winning the sugar bowl, pac 10 deciding to expand right when Utah was at it's high point in football history, Texas and OU deciding not to join the pac 12, Utah convincing the pac 12 to add them.

A lot went right for TCU as well:

Hiring Gary Patterson, joining the MWC to raise their status, beating Wisconsin in the Rose Bowl, somehow not letting Patterson get hired away, A&M, Missouri, Nebraska and Colorado leaving the big 12 right when TCU was at it's high point in its football history, and some how convincing the big 12 to add them.

I don't think BYU could have done anything different in order to be added to the Pac 12 or Big 12 though, maybe win 3 national championships in a row or something crazy like that. They proved they were winners, they have a strong sports program, and they still couldn't get added.