If it were up to me the Big 12 would have 8 conference games. Tell me which conferences have been left out of the playoff and notice a pattern (They all have 9 conference games) Heck, Notre Dame did not even play the magical 13th game last season (Title game) and still got into the playoff.
You need quality wins for the playoffs, how do you get quality wins? You beat a team that ends up above .500. Beating a 7-5 Akron team is considered a quality win whereas beating a 6-6 Kansas State team is not. If the SEC or ACC went to 9 conference games, that guarantees one more loss for half the teams, you know what else that does? It drops the probability that SEC schools get a quality win. Kentucky can go 4-0 in non-con and finish 7-5. If Alabama beats them, it is a quality win for Alabama. Let's say Kentucky goes 3-0 in non-con and then 3-6 in the league because they have to play LSU instead of Tulane. They are now NOT a quality win that Alabama (or anyone in the SEC) can count towards their resume.
I know some folks slobber over the round robin of the Big 12 but you are shooting yourself in the foot by doing it as far as college football playoff hopes go. I'd rather almost guarantee a playoff berth than thump my chest about having a 'tough out' in the league This can have an impact on revenue. Ask the Pac-12, they are really hurting and not getting that playoff money leaves a mark. (I know it is not their biggest issue but does play a part)