It's not OL across the board though, it's specific to LT & to a lesser extent RT.
LG, C & RG are much easier to develop than the Tackle positions.
DL is a difficult to develop PHYSICALLY, because freak athletes on that side of the ball are rare & it's a mixture of genetics combined with a good strength program to get them to maximum level of their potential.
But in terms of COACHING, DLine Coaching isn't on the same level as QB, OL, WR, CB & Safety COACHING in terms of technical ability & teaching.
There is nothing that you can teach an undersized & badly built kid to play like Jordan Davis or Jalen Carter. Those two dudes are just genetic freaks of nature.
Do you think Gregory Rousseau got some kinda special teaching at Miami that he wouldn't have gotten anywhere else that made him into a 1st rounder? I mean considering the 3 different DL coaches he had during his time in Miami, I'm not sure what secret recipe each coach passed down to the other, but I think him being a 6'7 freak of nature had something to do with it.