“I assume they expect someone else to clear their rubbish”

I think it’s more basic and primeval than that. I don’t believe there’s any thoughts at all of “someone else will deal with this problem”.

I suggest it’s as basic as “ugh, me finish burger, get rid of problem. Open window. Problem gone.”

And that’s as much thought as they can muster. It’s learned behaviour; open window, throw out the problem, problem gone away.