They have so many rooms per night they give away for redemptions and then I'm sure the rest they would like money for, considering they probably wanna be able to keep the property and the lights on so they have to pay the bills, not very profitable to give every room away for free. You might get lucky though and like a couple days before they might open some up. Happened to me a couple times, nothing available for weeks and weeks before. Two days before the trip i checked again and BINGO some opened up