I think you’re looking at it too narrowly. Yes, there clearly is a shortage of NCAA head coaches good enough to win a championship. Remember that many of the championships over the past couple decades were won by guys who are no longer coaching, such as Sabin, Myer and Orgeron. (I’m too lazy to look it up, but maybe even the majority of championship coaches in the 21st century are no longer on the sidelines?)
But the shortage doesn’t stop with championship head coaches. There’s also a critical shortage of little known, almost behind the scenes guys who can, wholly on their own without head coach knowledge or guidance, create cheating schemes to win games and championships. Those guys work cheap and can keep the cost of head coaches more reasonable…..if a program is sleazy or lucky enough to find one!