Offensive linemen are the weakest athletes on the team next to kickers so it's not shocking that many of the very effective pumped-up college overachieving types do not make it in the NFL and often aren't drafted. That goes back to the Osborne Nebraska team and earlier. I remember following Oklahoma in the '70s during the awesome wishbone era with 400 to 500 yards rushing per game as norm. They had some linemen picked late in the 17 round draft but rarely if ever had an elite pick.
Likewise with current Alabama and Wisconsin. Those are terrific collegiate offensive lines but they devote years to shaping themselves into the proper size and strength for the position, often maxed out as collegians. Wisconsin just had one of its long time starters at offensive line retire due to injuries.
I'm a bit more surprised at Stanford. They have had some very highly rated recruits at offensive line, 4 and 5 star players. But it is a recent development and may not translate to those numbers yet. Besides, as I mentioned last season David Shaw doesn't know what he wants to do on offense any more. Everyone sticks to an image of Stanford aa a blue collar I formation running team but they had the second fewest rushing attempts per game of any team in the nation in 2018, ahead of only Mike Leach.
The Canes have plenty of guys who are obviously talented enough but they aren't in ideal shape and we never have an identity that features them. It has been hodge podge offense for a decade or more. Normally I scoff at the notion of not developing players fully enough, but it is certainly true at offensive line. Often I'll see a guy who looks good as a sophomore and then he looks identical as a senior, if not worse.