I think it was because people were looking for some kind of thrill and escape after the war. Maybe the mystery and spookiness of ghost stories offered a break from the harsh realities of the time.
Well, one reason could be that the post-war period brought a lot of uncertainty and fear. Ghost stories gave people a way to confront and deal with those emotions in a fictional setting. Also, there might have been a lack of other forms of entertainment, making ghost stories more appealing.
The popularity of ghost stories in the late 1940s might have been due to a combination of factors. Maybe it was the cultural climate, where people were more interested in the supernatural. Or perhaps it was because they provided a form of entertainment that was both exciting and somewhat comforting in a time of change.