Sex and horror are strange bedfellows. As types of entertainment that exist outside of the mainstream’s safe zone, they’re inexorably linked, but they also have an uncomfortable relationship with each other. One of the most referred-to stereotypes in horror movies, and particularly slasher movies, is that if a character has sex on-screen, or has ever had sex in their fictional life, they are going to die. Films like the Friday The 13th series, where it seemed like Jason Voorhees had a sixth sense for people fucking nearby (an idea that became literal with Jason X).
Now, while there’s a general understanding that, yeah, that’s the actions and motives of the villain, so it’s not implicitly meant to be a viewpoint that should be adhered to… well, when it gets to the point where that stereotype of ‘sluts die’ is something that gets brought up consistently not just with discussions of older films, but is brought back in a lot of modern meta-horror features as well, you have to start wondering if that repetition is to acknowledge how regressive that worldview is, or to reinforce it. See also: The black man being the first to die in a horror film.