Dirty cities aren’t a matter of people cleaning them so much as industrial processes and car fumes not dirtying them.

There’s also the different materials they use - everything in Tokyo is covered in concrete (not sure if that’s good or bad) but buildings also strangely tend to be covered in what I’d describe as bathroom tiles. I wondered about this, but realized it’s just so humid they’d be growing mold otherwise.

Also if you’re comparing to NYC, it’s just particularly dirty because everyone leaves their garbage on the street, since the government is incapable of organizing anything better.