I suspect that a lot of it has to do with the fact that density is expensive in terms of building and infrastructure and also that many people don&#x27;t especially want density as a matter of choice. As a result, most cities that have highly dense areas largely created those after they had already built out into surrounding areas. (The somewhat exceptions are geographically constrained areas. Even pre-skyscrapers there were very dense areas on Manhattan like the Lower East Side although presumably a return to tenement living conditions isn&#x27;t a desirable future for cities.)