A sense of helplessness also makes a scary story scary. If the characters in the story can't do anything to escape the horror that's coming for them. Like in a haunted house story where no matter how hard they try to run away, they keep getting pulled back in. The feeling that there's no way out is really spooky.
Realism can be a big factor in a scary story. When the story has elements that could potentially happen in real life, it becomes scarier. For instance, a story about a serial killer on the loose in a small town where people go about their daily lives not knowing they're in danger. It makes you think that it could happen to you or someone you know.
What makes a scary story truly scary is the element of the unknown. When there are things that are left to the imagination, it scares people more. For example, in a story where there's a strange noise in the attic but you don't know what's causing it. It could be anything, and that uncertainty is terrifying.