Its not there's no trash, go there at night, especially on the weekends, trash, cig buds, bottles piled on the streets, alleys, etc. It's deep cleaned early in the morning.
Considering its population density, even at its worst Tokyo measures up pretty well.
My point was they do trash the streets, somewhat on purpose, during the day you don't, but at night it's okay to pile the trash near the other piles of trash. It's only clean because they clean it thoroughly. Any other city could have that same staff and keep a city clean like that.
It's not culture specifically, it's city management.