Well, a couple of possibilities come to mind. Maybe this is a coaching staff that isn't all that great at evaluating talent. It could also be, to some extent, that the physically gifted aren't terribly good football players. My own experience was that the best natural athletes I've ever been around weren't necessarily great students of the game, and if they didn't have the physical advantage could be out-strategized and out-executed. (I sound like Bob, but there's a lot of truth there.) I think that's why great, notable players for the most part don't make very good coaches, because they just do what they do. Whereas the less gifted have to work at it really hard and can find a way to become a better player.
The ones who can convey that knowledge to players and get results make for very good coaches. There's also the issue of motivation. I'm not sure Bob is all that great a motivator, though I see him trying.
I know both Bob and Mike were pretty good to very good DBs, 30-plus years ago. Not so sure they're great coaches especially at their positions. Cale Gundy seems to be a good coach though he's coaching a position he didn't play. Josh Heupel does okay strictly as a QB guy but his record as an OC calling the plays is...mixed, to say the least.
I dunno. I think we're all looking for answers. It may be something as simple as key elements of the coaching staff working with players to modify their skills and them never getting over the hump--or it takes a long time to get there--and in college you simply don't have the time for development. Or not much time. Or the personnel.
Example: our top WR is returning punts. He gets injured. Now we've got our top DB catching punts. Forget returning one because the absolute last thing the D needs is for Sanchez to get dinged up (further than he was). All I can figure is we don't have anybody else on a roster of 85 players who can catch a punt? Apparently so.