The issue of low income housing in the US is complicated by government interventions as well. Laws intended to benefit low income tenants, such as rent control, eventually result in less interest by landlords in maintaining older buildings, because there is no profit in it -- and it may even entail a loss. This can lead to some of the symptoms of degradation of the property and the community surrounding it that you described in your post. This eventually leads to the demolition of the buildings, the upgrading of the neighborhoods, and the displacement of the tenants. Trying to completely shelter the tenants from the marketplace rarely helps to maintain the low income housing.