Genre hybridization as deliberate technique
The new weird's fusion of fantasy, horror, and science fiction is not accidental eclecticism but a deliberate technique: each genre's conventions are brought to bear on the story's world in specific ways, and the result is a world that cannot be fully contained by any single genre's expectations. Fantasy contributes secondary world coherence and the logic of magic and non-human species. Horror contributes genuine threat, the corruption of the familiar, and the specific quality of dread. Science fiction contributes the extrapolative logic of how strange things would actually function in a consistent world. The new weird author must have sufficient command of all three genres to use them deliberately rather than accidentally.