unlike the "everybody's welcome" approach of the NCAA tournament. That's the stated goal. The unstated aim is to keep the "BCS busters" out.
It's all about power. The P5 have excluded the NCAA from CFP and they are not about to weaken its stranglehold on the post season by watering down CFP
What happens after 2025 is unknown but
the playoff will stay at four through the length of the contract.