It’s business. Hollywood isn’t planning to give you a nitty-gritty actual horror TV/Movie show without attracting the masses with widely acceptable aesthetic. There has to be a pretty girl or a handsome guy because aside from them, what else is there to the product? A good plot line? Who needs that? As hurtful as it sounds, media is this way for your time to move faster than a Japanese bullet train. You don’t have time for a deep plot line and neither does Hollywood. The closest we ever got to true horror is American Horror Story and Hannibal.
As for books, almost the same thing except there’s an actual plot line. Young Adult is where the money is these days and teenagers clutch onto whatever hot guy they can find. If your main character is a girl, well you have to make her look fabulous for the hot guy in the story to notice her.
But honestly, I don’t mind. Media is fulfilling its purpose. No one is getting hurt in the process. I’m perfectly fine hugging my laptop’s screen showcasing Ian Somerhalder’s hot bod.