TL,DR: Both Utah and TCU were added when conferences HAD to expand - either for survival (TCU to Big 12) or for a conference championship game (Utah to PAC12).  Among the feasible options at the time, they were the clear best choice for those conferences.  It certainly helped that they were good, but that only mattered due to a lack of alternatives that could provide more.

For Utah:

The PAC12 wanted a championship game. That required 12 teams at the time. So the first choice was to take from the Big 12. But they tried that and only got 1 (Colorado) so they needed one more.

Options then that would somewhat fit the geographic footprint (which mattered at the time even if it apparantly no longer does)

• Utah... medium market, very good team with high public profile wins, limited history, meets research-focused academic requirements of the conference
• BYU... same (or smaller) market as Utah, very good team, strong history, undergraduate focus in academics, religious school with questionable cultural fit
• San Diego St... large market but already covered by USC/UCLA, very poor football, OK history, relatively poor academics
• Boise St... tiny market, very good team with high public profile wins, limited history, very poor academics
• Colorado St... medium market, mediocre team and history, meets research-focused academic requirements of the conference
• UNLV... large market, terrible team and history, surprisingly meets research-focused academic requirements, concerns with gambling and Las Vegas debauchery

If they needed another team, by process of elimination it pretty much HAD to be Utah (given the PAC12's priorities, I know we all think it should have been BYU instead)

For TCU:

Invited to the Big East in a desperation move just prior to the league disbanding as a football conference.  They weren't alone in this.  Cincy, UCF, and L'ville had already been invited and joined the conference.  Other schools that accepted invites (and never played in the conference) included USF, SMU, San Diego St, Air Force, Navy, Boise, Houston, Memphis.  BYU and Air Force were also invited and declined.  Eventually Tulane and East Carolina were added.  It's hard to argue the Big East was being super selective with who they were inviting.

So when the Big 12 lost 2 teams, they wanted to pull from an AQ (for reputation reasons)...  So the best options were those that were officially IN an AQ conference... meaning Cincy, UCF, L'ville, TCU or other Big East members.  If it had been a few years later, maybe Houston or Memphis enters the conversation, but at this point the selection pool was Big East teams.

Of those TCU had a larger population base than just about anyone and fit nicely into the Big 12 geographic footprint.  Only other options from that conference would be

• Cincy
• Louisville
• South Florida
• UConn
• Syracuse

Given geography and market size, TCU was a clear no-brainer.