Also the division of roles is far more specialized than say basketball. Only the QB might have a near/full picture.
Linebackers, as the captain of the defense, which requires a deep understanding of the offense as well, tend to end up coaching as well.
Football team coaching staff are almost like another team. Position coaches usually are ex players of that position but as you move up the chain it gets more into strategic management and thus by the HC level it's more of a manager role with architects underneath for offense and defense so less position technical knowledge more game knowledge.