That's one of the major differences with Japan too -- a lot of housing is not meant to be multigenerational; it's built with the knowledge that the next person to buy the lot will be tearing it down and building a new house.
A lot of the cheaper stuff in Tokyo is older wooden housing that either survived the firebombing or was tossed up cheaply in the post-war years, so it's very no-frills. My current apartment, for example, is raised about 30 cm off the ground with nothing around the actual building -- you can actually peer under the building and see the light from my kitchen going through the floorboards. There's storage built into the floor and if you pick it up, it just exposes a giant hole to the ground. No insulation, single-pane glass, a bathing room with rotting concrete and tile.
I'm not saying all old housing in the US is better, but I definitely feel like building codes and/or initial quality was much higher in the US, so you have more buildings that were able to last longer (or through survivorship bias, the ones that lasted this long are just better) -- but in Japan, for whatever reason, you have a lot of these (almost literal) shacks with uninsulated walls and corrugated plastic panels on the roofs or across the windows.