Does he have a Board of Trustees like BYU to keep happy? Has he had to recruit around missions and the honor code? How adept is he at dealing with off-field problems? Does he have any real interest in coming to BYU beyond your assertion that he "loves" BYU?
Being a coordinator is one thing but a head coach is quite another. What "obvious" evidence is there that he can manage a program, especially one as unique as BYU's? One of the complaints against Mendenhall is that he can function well as a DC but lacks the ability to manage a program as a HC.