You don't understand what grant of rights means. It literally means you grant your rights to the conference. So, if you jump to a new conference, even if it pays you $100 million annually, you fork ALL OF IT over to your old conference. To my knowledge, the ACC agreement does not have a liquidated damages clause or "fines" provision that replaces the grant of rights. And it has a very long term.
Is it enforceable? Who knows? But my impression is that university presidents, regents, etc., are not the types to say, "**** it, let them sue us."
Often, the league will negotiate with the exiting member, the idea being "Let's not keep the exiting member another year or two more than they are contractually obligated." But the ACC deal runs through 2036. Not much room for bargaining. It will cost a pretty penny to exit.