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One of the things that doomed Josh McDaniels with the Denver Broncos was his reluctance to field a highly experienced coaching staff. In his first year, he could not coexist with defensive coordinator Mike Nolan, who turned that Broncos defense into one of the better ones in the league. In 2010, had two very inexperienced coordinators on both sides of the ball.
You need to have an experienced coaching staff in order to succeed in the NFL.
In college though, it's not as much of a mandate. The majority of assistance coaches in the NCAA do not have years of experience as an NFL head coach or coordinator. On the college level, McDaniels can simply put together a staff that can focus on teaching the players while he focuses on strategy.