joined the WCC that there was language in the agreement that BYU only guaranteed that they would stay in the WCC a certain number of years and that after that period of time they could leave without penalty, as long as it was for a P5 conference. Am I making this up? I swear the WCC commissioner at the time said something like "we may not have BYU for long but we'll enjoy it while we do".

Of course some later agreement may have been made that nullified the original.