What if they did? In what way does this harm you?
At one time they said the same thing about exposing any skin at all even at the beach.
Every human, yes including children gasp has a body with body parts, so mere exposure to the sight of them and knowledge of their existance is not harmful. Sight of the act of sex is merely more of the same. Kids on farms see it every day from birth.
At worst it's perhaps distasteful or lacks appropriate decorum in some contexts. I find practically everyone to lack taste or decorum in most WalMarts. It's not a valid argument.
It's only worth about as much legal consequence as defecating in the wrong place. In fact defecating is worth more since it at least carries an actual public health consequence to others beyond "I don't want to see that"
"I don't want to see that" is an utterly invalid demand, since anyone can say that about anyone for any reason. They used to be able to say it about merely being a mixed race couple in public, or hell a lot of people still do say it about gay couples or trans individuals merely existing in the room. It is ever so slowly being recognized that in order to try to claim any kind of say over anyone else like that, you have to show harm, and no one can show any harm from a person merely existing as gay or trans or black or female etc. Anything you can say about how obviously depraved and harmful it would be to see naked people or sex acts in public, used to be said about all kinds of ordinary harmless things. People were imprisoned or killed over nothing but "I don't want to see that" and "I don't like it that that exists" without any actual harm to justify it.
Talking this way about sex work and evidense of sex work being visible in public, is exactly the same.