A big part of this has to do with zoning laws. In Japan, zoning is largely done by gauging the externalities produced (e.g. noise, pollution, foot traffic, buil

A big part of this has to do with zoning laws. In Japan, zoning is largely done by gauging the externalities produced (e.g. noise, pollution, foot traffic, building height, etc), whereas in the US, zoning is largely done by function (housing, commercial, industrial, etc). So in Japan, you have many neighborhoods that have a house beside a tea shop beside a tailor beside house. In the US, it is very rare to find such mixes.