This is an interesting thread. The problem is instincts. An analogy to the problem would be to think about a building. Every player has a ceiling for their potential, and all coaching can do is help you reach your ceiling. It cannot change what floor you on. Therefore one of the problems we face in Mississippi is that we are capable of producing players that have a high "floor" of athleticism, but don't reach their "ceiling" until later in their careers because of the lack of quality year around youth football programs.
You really see a lot of this issue in baseball with youth teams from Florida and California. Because of the weather, kids from Cal and FL are able to play baseball year around and thus reach their ceiling as players much earlier than Mississippi kids. This is why FL and Cal high school baseball is much better than any other states. However, MLB has players from all states and Canada because, ultimately, players can get no better than the floor of their athleticism, but because FL and Cal youth have developed instincts and reach their ceiling earlier because of playing more, they usually dominate youth baseball, Little League World Series, and High School baseball.
Due to all this, Mississippi High School coaches are dealing with many players that have played very little organized football, and lack the instincts, knowledge of the game, and basic fundamentals to run anything more than a basic offense. Now most of our players will reach their ceiling, but it will take at least 3 years of college to get close it due to all the problems I have mentioned. That is why we always have very little depth. We have young guys, but they simply are not ready to play.