2. Health concerns: At last check, the NCAA was fighting scores of head trauma-related lawsuits. Last year, the Chicago Tribune predicted at least 40 were forthcoming. Mix that in with the fact an eight-team playoff would guarantee the two finalists would be playing 16 games. That's an NFL regular season for young adult bodies with brains that aren't fully developed by their mid-20s.
Adding games adds more chance for injury. The more chance for injury, the more schools and the NCAA are liable. The NCAA is deeply involved in head trauma research with the Department of Defense. As part of a lawsuit settlement, it is in the middle of paying $70 million to set up a medical monitoring plan over the next 50 years, after paying $75 million to that class. The NCAA Oversight Committee is looking at ways to reduce injury risk, including a general conversation about eliminating kickoffs. More football is not the answer. Health is probably the biggest hurdle to expand the playoff.
https://www.cbssports.com/college-football/news/heres-why-there-will-not-be-an-eight-team-college-football-playoff-anytime-soon/
There's a lot that goes into this the just playing another game. Insurance liabilities play a role especially considering a lot of the athletes playing the extra games are future millionaires
Now, I understand those are hurdles that can be overcome, but why bother when the system works for you? No undefeated power five school has been left out. They are all ok with win all your games or take what you get. One always eliminates itself like the PAC-12 did this year anyway.