The contracts allowed the league to add teams and required the networks to pay more money.
However, the networks told the league the demand wasn’t there and the increased amount wasn’t justified. This is when everyone was cord cutting and the networks realized they way over paid for TV rights.
The Big 12 could have held the TV partners’ feet to the fire but they would be slitting their own throats down the road when it was time to renegotiate the next round of TV contracts.