do people not notice the sounds coming from them

Yaoi logic

nah, almost every smutty literature has this kind of logic. straight or nah

Smutty litterature evolves in a different world, where everyone is blind and deaf ╮(￣▽￣)╭

Japanese culture is to not look or stare at a stranger. They mind their own business unless his moaning causes a scene, then they'll react. But 99% of the time, Japanese ppl mind their own business

Hmm, while I do believe that they mind their own business, and although I am no law expert, I'm pretty sure having sex in a public space in a situation in which it can bother other people (not everyone wants a slice of the salaryman next to them's sexlife for breakfast) is illegal and punishable by law, just like flashing is.

I really think this recurrent theme has more to do with the fact that they are known for being more discreet with their relationship in public, which, like anything that is meant to stay "hidden" transforms public display of affection (and more) into a taboo. Taboo and fetishes can be deeply linked, actually most most common fetishes are deeply rooted into different taboos (doing it in a public space, risking being seen, wanting to be tied up or to tie up, doing it with more than one partner, etc.)

Anyways, that's my theory, don't take my word for it, I'm no sociologist (⌒▽⌒)

They notice, they didnt care coz they are busy people(￣∇￣")