Exactly. The beach is one thing, everybody is wearing a bathing suit. Walking downtown, you're gonna stand out. Or it could be that the underwear is pretty much either unattractive and functional, or see-through because they are meant to be covered by clothing. They really are two different things. You swim in your underwear and you might as well be naked, since it's going to be clinging and see-through.
that's a fair point, no-one bats an eyelid if a women is by the beach in a string bikini, well not in Europe anyway. Sometimes in Magaluf (Majorca) you can see women from the beach walking around the main street or bars in pretty skimpy bikinis or outfits.