OK, so a little investigation turns up something in the NCAA bylaws. Specifically "NCAA Bylaw 30.15 Summer Basketball".
f) Revenue. No admission shall be charged for any game, no fee shall be charged for parking to attend any game, no revenue shall be realized at any game from raffles or similar activities, and no revenue shall be realized from the over-the-air or cable television or radio rights fees for any game.
Sure it's only $5. But if I was a cynic, I might suspect that the NCAA was very concerned to make sure that no one makes any money off an NCAA athlete except the NCAA. Precedents are precedents, after all.
If I was a cynic.