> It baffles me how the US has no shops / restaurants / convenience stores in residential areas and nobody questioned it over half a century.

That's definitely not true. It's not the norm, but I can think of plenty of places I've lived or visited that had neighborhoods that were a mix of residential and shops.

Here's an example of an area like that in Portland: https://www.google.com/maps/@45.5627602,-122.6949984,3a,75y,...