Quibble- all of them looked good when they first hit the field. They have got worse with more time in the system, imho. So I don't think it is the players themselves per se.
How many OL have we had in the past 5 years that when they first got on the field, we thought "that kid will be a solid piece next year" and then ended up disappointed in the total lack of improvement? A few had career-affecting injuries, but a lot of them just never took the next step.
Miller, Remsberg, Simmons, Newell, Foster, Ramos, et al
IDK if it the OL scheme, how they teach it, how they practice it, if it is too complicated, too simple, or WHAT. But the development of the OL players, and the performance of that unit, has been very poor. Especially the last 2-3 seasons.