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It’s not just a certain group.
It’s amateur coaches thinking they’re professionals.
Many NFL coaches started off coaching in college and/or played in college. They all have to make the transition to the NFL at some point. Some do it earlier than others and I think it's easier to learn to coach in the NFL by being an NFL assistant rather than trying to go from college HC to NFL HC, but as the college game gets closer to the NFL game with kids making large sums of money, I think you may end up with more college coaches that can make the transition. Plus, it seems that the NFL keeps incorporating more and more pieces of college offensive schemes into the NFL.
I'm still highly skeptical of any college coach being a good NFL head coach, but it does happen.