The TV contracts are buying the big games from the conference which alone would cost more than their $4M-$10M average price. They're buying the big games from the conference. Buying the conference ensures them they will get to pick some good games based upon which teams they're doing. Look at the Big 12. What if Texas had gone alone? They would've had over paid for some bad games but luckily Baylor became good during that time and TCU.
Getting the conference is like hedging your contracted games.