The expressway + car infrastructure to support suburban development was not cheap. It was in no ways organic. It was supported by the FHA's race-based redlining policies and banks that gave loans in the post-war era to white GIs to build homes in white-only suburbs.
Cars revolutionized society in a lot of ways. They're cheap and opened up possibilities that were unthinkable beforehand. Greenfield building is cheaper and easier than retrofitting, and since real estate cartels typically dominate urban real estate, city life is always more expensive than the bigger, nicer and more stable suburban home.
A lot of things happened in the postwar era beyond redlining. The poor Italians, Irish, Jews and Polish who lived in the tenements started making more money and slighter better opportunity. Jim Crow sparked a great migration of blacks from the south northward. Government thought that bulldozing tenements would fix problems.
>since real estate cartels typically dominate urban real estate
Perhaps had all the resources of government been focused on fixing this problem instead of confining black and brown people to and divesting from the inner cities, we might have more affordable, walkable, dense, valuable, resource-efficient, revenue-positive neighborhoods today.
http://articles.chicagotribune.com/2011-12-18/site/ct-per-fl...
https://en.wikipedia.org/wiki/Redlining
>Moreover, cities were increasingly discouraging tenements...with sound scientific reasoning.
Please cite said "scientific" reasoning.