I think the worry, iirc, was that the Big12 could've deteriorated and been raided by the schools to the east for scraps had TX and OK bolted for the PAC 12. Potentially, it could have left BYU in a new conference with the Iowa and KS schools and perhaps some AAC schools.

Whether that would've still been better than the MWC today or Indy is debatable, but I can appreciate BYU's dilemma at the time, even in light of the point you raise.