I'm gonna blow your mind a bit, but it's because they build homes and don't let local obstructionism stop them.
I wanted to include these graphs just so you can clearly see that Japan has had noticable success compared to others. Although the US is unique in our misunderstanding of the situation.
"If you want to know how powerful the European dream still is, don’t go to Paris or Rome, Brussels or Berlin—go to Kyiv." -- @rcbregman, author of HUMANKIND, writes about Ukraine and the EU for @TheAtlantic.
Bregman goes on: "Or as an American would say: 'Ich bin ein Europäer.'"
Love the pic at the bottom
On the Japanese home building thing, part of the reason as well that buildings go up so quickly (and we're talking 3 stories or fewer) is, perhaps unexpectedly, the lack of good construction quality. For example, it's very likely your Tokyo home may not be insulated, which would help keep cooling costs down in the summer, but it's "just not done." It's much more likely Japan will be willing to burn a bunch more energy cooling and heating than they would building their homes better. This also marries to a number of cultural norms around putting up with things (they would literally announce they were cutting AC in the airport to save energy because of the grid getting overloaded), as well as around Shinto ideas about spirits inhabiting buildings and thus a family would like a new home built in place of an old one. Of course, we are gaijin and don't really know what we're talking about.
The only places that care about insulation in Japan, apparently, are places cold enough where it's critical like Hokkaido in the north. I can't find it at the moment, but I once had a great breakdown comparing American construction standards (which have their own issues) to Japanese ones, particularly with the experience of building/renovating for an American who moved to Japan. I think one couldn't even get insulation shipped down from Hokkaido for a reasonable price even if he could get his builders to install it.