Gen Z is turned off by onscreen sex, wants no-mance over romance, a new study finds

This is definitely a cultural prudishness emerging. But that's only part of it. There has also been a shift away from artistic filmmaking and toward high-grossing tentpole movies. Because nudity is a taboo in our society, you need an artistic purpose to the nudity (or sex scene) in the film or it won't serve any purpose to the film, and people will notice that it's out of place. If most of the movies you have are cookie-cutter concept movies with little to no artistic expression, you just can't make anything taboo work in them.

Obviously everyone has different taste in movies, but some films that made on-screen sex work really well are Basic Instinct, Blue Velvet, and Eyes Wide Shut. It also adds a lot to really campy movies. Nightmare on Elm Street comes to mind. Species became a cult classic because of its use of nudity and sex. For just plain nudity, It Follows used it well in the briefest of glimpses of the antagonist. It also added a lot to Ex Machina.

Those are just the movies off the top of my head that were made more impactful by sex and nudity.

Oh! Airplane also has a big laugh thanks to a scene of gratuitous nudity. Let's not forget the comedies!