Very, very basically, it is kind of two fold:
1 - since the last contract, teams not named Texas and Oklahoma have increased fan engagement by 40% against each other. Parity in competition helps this, but also do large fanbases who care about sports. They're not brands, but they're competitive.
2 - They likely were looking at a $60m contract with Texas and OU. The B12 had never had a moment where it took all of its rights to market at the same time and their T1 deal was horribly undervalued. They were set for a big bump in 2025, not B1G/SEC bump, but much bigger than they just received.
So, the continuing of the old terms factors the loss of Texas/OU plus the gain of new engagement into the new deal. $32m is the broadcast in year one, which will increase. The rest is post season, March Madness, etc.
Also, on the seats comment, this one always throws me off. Most big games, in general, not just the Big 12, are not reliant on traveling fans. In fact, I think the B12 only allocates like 2-3k seats to the opposing team in far flung corners. Anything else is usually season ticket holders unloading to travelers. Unless you're saying they only fill up for big games, but that doesn't seem to be the case. Most are close to capacity for the entire season, not just a few games.