Earlier quoted context omitted.
The USA does export its drug policy stance, and per the Nixon policies, it's a win for any government to have those tools of oppression on tap for when needed.
I think a simpler explanation is that the general public in a country such as Japan deeply hates drug use.
The deal is lack of education, and exposure. The west is a lot further along on the pathway to legalization. I do believe that when the day comes, usage will be similar to in the west under legalization. We are all humans after all.