Cannibalism goes back a long way. It isn’t surprising that cannibal horror movies and stories about cannibalism have existed for a long time as well. Stories and myths that involve human flesh go back to ancient times. From Hansel and Gretel and Baba Yaga of Slavic lore to even earlier Greek and Roman myths such as Saturn devouring his son.
It is foundational for a disturbing idea like cannibalism to be a fixture of the human psyche. And natural for it to be a part of human storytelling.