Horror movies started to wane around the onset of World War II, and after World War II, when all the troops came home, people weren't really interested in seeing horror movies, because they had the real horror right on their front doorsteps.
“Art is the most beautiful deception of all. And although people try to incorporate the everyday events of life in it, we must hope that it will remain a deception lest it become a utilitarian thing, sad as a factory.”