With rich folklore traditions why have movies collapsed to just a few monsters?

We have about a million films showing vampires, zombies, werewolves, and ghosts.

But despite rich folklore traditions we see very few films about other creatures. There is a handful of films dealing with leprechauns, pixies, trolls, fairies, witches, goblins, gnomes, etc. And that's just the western traditions. We have huge range of unexplored creatures from around the world. If I had to sit through yet another vampire film I'd rather it was based on adze traditions than Bram Stoker reinventions.

Why are there so many films that tread the same ground about vampires, zombies, and ghosts, and so few films about everything else?