Just because the Big 12 isn't convinced today doesn't mean things won't change in 6 months or a year.
I never expected a Big 12 invite this year, but if the Big 12 finds out that dropping its championship game comes at a huge cost, it will come calling. The only reason they don't want 12 teams is money, and if BYU brings its share plus the Big 12 game back, that's going to convince a lot of people.
If something huge happens, like Texas A&M defecting to the SEC, then they will be scrambling and BYU will be #1 on the list.