playoffs every year. They've monopolized the process and are getting the highest rated recruiting classes because they're able to sell the best 5* recruits the playoff experience. Increase it to eight teams and that selling point isn't as valid.
And if some random team gets in and has to beat three top 5 teams rather than two, so be it. I don't want an inferior team to fall bassackwards into a National Championship with a little luck. I want them to earn it by beating the best teams.