My theory on it is alot of players that fizzle out in the league become coaches. You see alot more AA players than anyone else in the league and they stay around for years making millions of dollars. Alot of them want to just retire and be with their families once their playing career is over as they already have all the money they could ever want. Not the same for players that fizzled out in the league and didn’t make that money, not because they weren’t smart, but because they just didn’t have the athletic ability to make it (Sean, Kellen etc).
I also believe you see more guys that were QB’s and LB’ers as coaches, they tend to be the smartest guys on the field.