reward of anything else. That and the lack of depth at any given position group(s) from year to year. And to counteract that Bronco has indeed done a fine job of creating a model that compensates for that.
It seems like you are assuming that the coaches aren't doing what you described in your post. I've been to A LOT of practices, these guys do get drilled over and over and over again, watch film over and over, are encouraged to watch more on their own, etc. And I'm keeping in mind that this is Howell's first go around as DC.
I liken it to the bball team where I have seen coach Pope work large chunks of practice on post moves with the big men, only to see them get the ball down low in a game and look like they've never seen a basketball before. Now you can say, well that's on coach Pope for recruiting those guys then. But while that's partially true, it isn't that simple imo.