There's actually a lot stopping it. First and foremost, reams of zoning and other regulations that are not easy to repeal. Second, the entire physical environme

There's actually a lot stopping it. First and foremost, reams of zoning and other regulations that are not easy to repeal. Second, the entire physical environment poured in concrete which is expensive and difficult to retrofit well. The street patterns of suburbia are hostile to walkability because they intentionally increase the distance between points with poor connectivity and dendritic routing. This is why the majority of suburban areas decline after the first generation of development and never revitalize.