You can't use the OAD argument here because that is an NBA rule. As far as the NCAA is concerned (so they'll tell you), all these freshman could go straight to the NBA. But since they can't do that, because the NBA says they must be a year removed from high school, then the kids must play by the NCAA's rules.
I'm sure they could find a way to make the programs (and even the players) respect the spirit of the concept of "student-athlete" and cut-down on the 18 and 19 year old guns for hire even if they can't coordinate with the NBA. Better than throwing their hands up and blaming graduate transfers who earned their degree.