Sex sells, but when you oversaturate the market it loses its luster. Gen Z basically grew up in an age of sex-positivity where it went from "Sex is a thing, get over it" to a bunch of corporate bodies going "SEX SEX SEX SEX SEX SEX SEX!!!" for shock value and attention. Sex used to be taboo, it was the "adult thing", but now it's so fucking prevalent in like every form of media and everywhere online that Zoomers probably just don't give a shit about it anymore. Not in the 'asexual' sense, but in a capacity like you mentioned-- it serves no purpose. It's hamfisted. You shove sex into something for shock value, coomer attention, or to pad the runtime. It's like the "Stop posting about Among Us!" shit expect it's "Stop trying to shock people with sex scenes!"

It's not even puritanism, it's just that Zoomers are fucking sick of it.

I personally don't really have an issue with sex scenes themselves in movies/shows. The issue is that in many cases, when the fucking happens, the plot stops, and I'm less interested in your subpar porn attempt than I am in the plot.