With ESPN reporting that Texas A&M will in fact join the SEC, the likelihood of BYU getting an invite is quickly increasing. And although the money and BCS access might be hard to turn down, the exposure question remains.
Consider this: Big XII teams not named Texas or Oklahoma have 4-6 games scheduled on national TV so far for the season. Most of those games are against...you guessed it, Texas and Oklahoma. In fact, 5 teams still do not have a single game scheduled on national TV at all. Compare that to BYU's exposure in year one of independence with 10 games on the ESPN network and another against Oregon State likely to be picked up.
And then there's the question of BYUtv. BYU and its fans are very excited to have the rights to its games not broadcast on television, but the likelihood of that happening in the Big XII is slim. Indeed, the Longhorn Network is the very thing that pushed A&M over the edge. BYU has spent a lot of money and time to build up BYUtv to get ready for the sports season, and they aren't likely to let that go to waste.
Let's also not forget about the contracts BYU has signed pursuant to their declaration of independence. Getting ESPN to broadcast 3 or 4 games in the Big 12 shouldn't be hard, but BYU has committed to play too many teams to fit into a typical Big XII schedule. Take 2012, for example. That year they have contracted to play Oregon State, Hawaii, Utah, Boise State, Utah State, Georgia Tech, and Notre Dame (a great schedule, I might add). Clearly this wouldn't fit into their schedule as a Big XII member, so BYU would be forced to buy out of the contracts. It's doubtful that the Big XII would cough up the money to help with those costs.
Being in an AQ conference is worth a lot, but is it worth sacrificing the exposure and schedule independence has already given the Cougars? Probably not.