Common misconception. Japan can be very trashy, especially in big cities. It doesn't help that the government doesn't put public trash bins anywhere, supposedly because they're scared of terrorists putting bombs in them.

Even in the suburbs and countryside, people illegally dump trash all the time because they don't want to pay to dispose of it properly. Anywhere you go, you will see signs imploring, "don't throw away your trash here!" under which are mounds of trash.

It may be true that Japan is on average a bit cleaner than other countries, but not nearly so much as people seem to think.

Yeah, but there are almost no public trash cans anywhere. Lots of bins for bottles and cans though.

And now you know why!