The concession part isn't true, and giving away 3k in tickets would potentially cannibalize current season tickets/flex plans/group tickets. Maybe for a game like Holy Cross it makes a little sense. But every game? It's not a good business model.
Show rate for free tickets is usually around 50-60%. Plus, for the Clemson game, and potentially down the stretch, it's likely that those tickets would be sold, so we'd be losing money.
Fact of the matter is, unless you're only interested in making the stadium look nice on TV, it's a better business model to let the seats go unsold.