Isn't it because they have armies of cleaning people in the streets ? A friend of mine told me about it, I think he was in South Korea, Seoul perhaps, at the time. He told me people mostly act the same but their cities are more efficient at cleaning the mess before it piles up. I don't know if there are other laws similar to that [0] but it probably explain some behaviours too.

I agree with the underlying point though, some people just don't give a shit. I visited a small greek island last year and was appalled to see that locals were throwing their trash, old furnitures, construction materials, &c. over a cliff, straight to the ocean.

[0] https://en.wikipedia.org/wiki/Chewing_gum_ban_in_Singapore