I have seen other cases where this "demand" part of the equation was really "would like to buy a house, especially if it means moving out of the broken-down city" ... in the area where I grew up (Buffalo, NY), there was big "demand" for housing even though the county-wide population was pretty stable over 20 years: but the new houses were in the suburbs, and so even though moving from one to the other doesn't do anything to the "supply" (now there's an empty house that they left), the one in the city didn't get sold, it got abandoned.