And if we draft a player who isn't good enough to be a starting left tackle then we still don't have one. Drafting a player at a position doesn't fix that position unless the guy can play.
If they think that Campbell or any other LT prospect is going to be good there, then that should be the pick. But there are very real concerns about this OT class. Campbell and Banks are widely considered as guys who might need to move inside. Membou is a career RT who, even if he does end up a good LT, is likely going to be raw there so unlikely to be a day 1 fix that everyone wants anyway. Simmons will likely be a medical redshirt rookie so doesn't do anything to address the immediate need everyone wants to reach for anyway. The other guys are all considered day 2 prospects who could get pushed into round 1 because of desperation at the position, not because of their own individual merits.
You can't just manifest a starting LT. There's a very real chance none are out there in this class. You can't just bury your head in the sand on that. You know what's worse than having no starting LT? Not having a starting LT even after you used your top draft pick on one.