I talked about coaching tree. Assistant coaches learn habits from their HCs. How to run practices, evaluate players, pick a staff, etc.
Diaz's first HC, Mack Brown, was at a school that has unlimited money. Brown managed to win 1 title at Texas in 17 years despite having the pick of any player in the country and a blank check. Then Diaz got himself fired.
His next HC was Mark Richt, who again, despite being at school that was among the richest in the SEC and had bag men buying any player he wanted only managed to win the SEC twice in 15 years. That's even without Saban in the conference for a couple years.
So its not a surprise that Diaz doesn't know how to build a program. He never really learned how. Yet this is the guy that Blake James decided to buy from Temple.