HC needs to have high end skills either running the offense or defense. He cannot simply rely on always having the best assistants around him. That ends up being an extremely expensive and risky model. It doesn't allow for sustained success.

That model requires BYU to go to market and constantly complete for the best assistants every few years. Whereas if the HC was extremely talented at running one side of the ball and teaching younger assistants his system, BYU would be able to grow talented assistants that by their nature would end up costing way less and be just as competent over time. Eventually they move on to be the high paid assistants at another school but it's more sustainable. This is how you grow a coaching tree.