This is happening, but it is only part of the problem. There are also developers sitting on land and waiting for prices to reach a certain level before they build housing on it. There is also the refusal of home owners to allow high density housing built next to them. Air B&Bs are a waste as well. All of these are property rights issues. If it is yours, you can do what you want with it and there is no limit on how much land a person or organization can own.