Initially at least, the Big 12's tv contract pays approximately the conference approximately $260 million per year. Break that into 11 pieces (10 teams + a share for the conference offices) and each school gets $23.6 million per year.

My understanding is that adding schools doesn't necessarily lead to automatic re-negotiations of the contract. If that is the case, and assuming they add 2 more schools, you now have $260 million divided into 13 pieces for 20 million per school. In order for the original 10 schools to maintain their payouts, they would need to increase overall revenue to around $307 million. Where would that additional $47 million in revenue come from?

Of course the conference could now have a championship game. The Pac-12 gets about $25 million for their CCG. Assume the same for the Big 12 and you are still $22 million short. Without the ability to re-negotiate the contract I have no idea where that comes from.

Utah was definitely in the right place at the right time. The (then) Pac-10 had a new, very aggressive commissioner, they wanted a championship game and needed to get to 12 teams, and it was time to negotiate a new tv deal. The attempted raid on the Big 12 failed and they considered Utah to be the next best option, and Utah was willing to forego full revenue sharing for a couple years in order to make it happen. Right place, right time. The same confluence of events and opportunities are not currently available to BYU, unless the Big 12 is forced to 12 teams in order to hold a championship game, and it doesn't appear as though there is too much pressure being applied currently to make this happen.