some rivalry games in the past that tickets were extremely popular and hard to get, but I always could get some through BYU.

I'm pretty sure the Big 12 isn't the one limiting what tickets they can give BYU because other schools give us plenty. I know schools like TCU have made it harder for BYU fans to get tickets, but they did that all on their own. I assume Utah is doing something similar now with BYU. Probably an extremely limited amount of tickets.