Punt returns aren't nearly as dangerous as kickoff returns. Kickoff returns were such a big issue that they first outlawed the wedge and then they moved the ball back up to the 35 to discourage returns. I understand there were even thoughts of eliminating the play altogether due to the high rate of injury.
The problem is that you have two teams of 230 to 280 pound guys running at each other at near full speed on KORs. I know people wax nostalgic about back when they played but players have gotten so much bigger and faster with modern training techniques that our cartilage, ligaments, tendons, bones and brains can't withstand the impacts generated anymore on such plays.