I totally understand, that you didn't keep on going to the hotel, after you've received the call, that they don't have a room for you. You were tired and you are obviously a kind person. But unfortunately in situations like that, it doesn't pay off to be kind. If you were going to the hotel and insisted on getting a room, you would have get one and/or a much better compensation. You have kept your kindness and get less compensation. Some say, that is a bad deal. Others say, that staying true to yourself is worth that money.

By the way: The DIA rules about compensation when being forced to walk away is just the minimum. If you have a reservation and they don't give you a room, you can always sue them - DIA or not. The hotel failed on providing you the main part of their service. That is not acceptable and there is no excuse for that.