If you understand the nuances of the NFL, then Gage not being drafted should not be a shock. He struggled at times against opponents that he should not have and he was most effective in run blocking, which is something that NFL coaches and scouts don’t care about anymore because the NFL is a passing league.
Cervenka had one shot to prove himself worthy and that was at Clemson’s pro-day and he failed to do so, he was not even able to match his own personal best in the 225 bench press. Clemson was one of just a few schools that had an actual pro-day and all 32 NFL teams had scouts, front office personnel, or coaches in attendance.