The only time i saw trash in Singapore (about 20 years ago) was after a Sunday movie night in the Indian section. Styrofoam food containers just tossed all over the field and other trash blowing in the wind.
Caste mentality - picking up after themselves is beneath them, that’s for the ‘other people’ to do.
In sociology classes, this is ‘their culture’, which is a fine way of being non-judgmental about their third-rate social structures.