Stephen King's clown horror novels are scary because he delves deep into our primal fears. Clowns are often meant to be fun, but when he twists them into menacing creatures, like Pennywise in 'It', it plays on our sense of the uncanny. The contrast between the expected jovial nature of a clown and the pure evil that his clowns represent is what makes it so frightening. Also, his ability to create a sense of dread and build suspense throughout the story keeps readers on edge from start to finish.
His use of psychological horror. For example, in his clown - themed works, the clown often targets the fears and insecurities of the characters. It's not just about a spooky - looking clown. It's about how the clown can get inside the heads of the people in the story and the readers too. The way King describes the clown's actions, the eerie settings where they appear, and the overall feeling of helplessness of the characters all contribute to the scariness.