When it comes to doing things the old fashioned way, hockey ranks only second to baseball. The old boys club still runs every organization, fighting is still allowed in the rules and coaching theory takes a millennia to evolve. It really took a coach thinking to figure out that a team should still forecheck on the penalty kill to pressure the other team’s players.
For whatever reason, the penalty kill is a space for bottom six players to try and do as little harm to the team as possible. This often results in a unit made up of some of the lesser quality players on the team.