Part of that comes down to, if there is controversy during these 12 years of a 4 team play off it would only boost the amount of TV revenues that may be available when they renegotiate at the end of 12 years.

If they were willing to change part way through this 12 years it may not result in as big of a contract as it would still be negotiations between the CFP (6 bowl chairmen) and ESPN - it would not be open to any additional bidders. Also it wouldn't have built up enough controversy to raise prices...

We should all accept that for the life of this 12 year contract it won't go to more than 4 teams. Other parameters may change for access/inclusion/etc but not increasing the number of playoff teams.