First, indefinitely is a long, long time. If you mean P5 literally then you are saying non of the current conferences will cease to exist or cease to play football. There are 3 conferences that have been major conferences for football bowl terms that no longer exist. The Big East is also an example of a major football conference that arose relatively recently (1979).
One very big factor for major college football is that is has become dominated by one region of the country. The SEC and the Southern portion of the ACC have dominated college football in the CFP era. The Big 10 and Notre Dame have large football followings and investment but are not on the same level competitively overall.
The growth of the Florida teams such as UCF over time will play a role together with the decline of the Pac 12 over several decades on the P5 structure.