The SEC expanded to 12 teams because NCAA rules said you had to have 12 teams to get the revenue for a championship game.
The ACC expanded to 12 teams because NCAA rules said you had to have 12 teams to get the revenue for a championship game.
The Big 10 expanded to 12 teams because NCAA rules said you had to have 12 teams to get the revenue for a championship game.
The Pac-12 expanded to 12 teams because NCAA rules said you had to have 12 teams to get the revenue for a championship game.
Then just before the Big 12 was about to reinstitute their championship game, the NCAA changed the rules and said they only needed 10 teams.
Sometimes you're just unlucky.