Do you know why some people really like mystery or romance? Or why others like science fiction or horror? The reasons are universal in that people all over the world respond to the genres because of the same reasons - reasons that speak to an individual on a sub-conscious level based on what the individual values.
Appeal of Different Genres
Science fiction appeals because of the desire for science or intellectualism to triumph over problems or challenges.
Romance appeals because of the desire for love and belonging.
Mystery appeals because of the desire for justice.
Fantasy appeals because of the desire for imagination and magic to conquer problems.
Horror appeals because of the desire for good to triumph over evil.
Now, you may not watch some spatter punk film or read some gross gore horror and see it as good triumphant over evil. Nevertheless, that is what it's all about.
You can take any horror book or film and boil it down to its basic components, and you'll find it's always a battle of good versus evil. At least the successful examples of this genre are. The unsuccessful examples probably were meant to be that, but somewhere along the way, the story had an identity crisis. probably because the writer didn't know the genre well enough to understand its dynamics.
Primitive To Contemporary
The horror story is ancient. I imagine some caveman telling stories around the campfire tried to scare the T-Rex out of his listeners. Horror connects with those not-so-logical parts of our brains. The primitive parts that tell us to get scared by what goes bump in the night. Stories from ancient times to today's urban myths are the end result, and people voluntarily listen, read, or watch in order to be frightened and to subsequently be reassured that good wins over the evil.
The Horror genre has always reflected the anxieties of each generation. In the original Dracula film Nosferatu, the story wasn't just about a vampire. It was a metaphor for the seemingly senseless and random deaths in the first world war and the later world flu epidemic.
The Dracula tale is told anew for each generation. Even George Hamilton's comic turn as the Count in Love at First Bite was a reflection of the superficial, hedonistic 1970s disco party decade and the greed-is-good 1980s that was rising.
What's really interesting is to take older horror films and contrast them with remakes to see what group stars as the villain and what the message is.
In previous decades, vampires, mummies, Wolf Man, and zombies starred as monsters. After the war with the threat of nuclear bombs, aliens and robots were the monster along with giant insects and other animals. All these reflected fears arising from the unknown. From UFOs to the effects of radiation, people were worried and writers and movie makers used this in their work.
Today, even with amazing visual effects, it's hard to create a really terrible monster when the evening news is full of stories about serial killers, war deaths, kids rampaging through schools, and parents murdering their own children. So tellers of tales ramp up the horror thus giving us Thomas Harris's books about Hannibal Lecter and movies like the Morgan Freeman-Brad Pitt flick Se7en.
Perhaps the last good monster flick was Alien and Aliens - forget any that followed those two in that series - and the Schwarzenegger flick Predator. What made those two films really scary and worthy of the horror label wasn't really the monster. It was the suspense as the monster picked the victims off one by one without the audience ever really seeing the monster.
In other words, it was the unknown, the fear of what goes bump in the night when you're imagining the absolute worst. And then you find out what you imagined wasn't nearly bad enough.
The horror storyteller must understand and respect the genre and stay true to its conventions, no matter how those conventions may be interpreted for contemporary audiences, then good will inevitably triumph over evil, and the resulting book or film will be a success.