The monsters you describe are part of the "gothic literature" of the 1800s and persist largely the same reasons we still watch movies or read books about human nature and such. The way horror challenges us, gothic literature explored human nature and often claimed to resolve issues of the nature of man, which is where the "flesh golem" of Frankenstein's monster derives; or the bestial force that exists within us in "The Strange Case of Dr Jekyll and Mr Hyde". Monsters like this are more popular tending to the fact that they are more human. There is nothing or little human about dragons or demons, they are perversions of the idea, and certainly anthropomorphic, but still not human.

The longevity of these things ultimately comes from the need for readers and viewers to somehow ensconce themselves in the often first person perspective of a man going mad, or whose been displaced, or is in a fight to the death with another half of his being. They are a way for us to.imagine ourselves without experiencing those actions explicitly. In a way, it's to players explore the pathway of humanity or inhumanity, including predaceous or perceptive avenues.

Fantasy itself has a similar ultimate theme, that of abnegation, wherein we can immerse into another place without worrying about it. But modern fantasy merges gothic themes, some horror, and "pure" or "epic" fantasy themes to evoke an escapism. The more successful ones are the ones that, oddly, describe the nature of the thing being depicted as simplistic, so the Wolfman is a savage carnivore, the Vampire is a sexual predator, Frankenstein's monster is an aberration of science, and therefore to be rejected. So here, you embrace fantasy themes, but reject gothic ones.

As a related followup, when were the first stories of Zombies, Werewolves and Vampires created?