Because there's the B side, dude. Werewolves and fairies and goblins are all acknowledgements that there is magic in the world, powers beyond our ken. That alone is a huge relief, a reassurance that fate doesn't rest solely in our ham-handed humanity. That there is, somehow, more if only we could see it. No other fictional form offers that kind of reassurance.
Westerns are about conquering other men and the environment itself.
Romances are about finding love and being safe. Mysteries are about the rightness of societal pacts. Science Fiction is an affirmation that you too can be popular if only you have super powers or a fast ship or an awesome command of mathematics. Even serious literary novels about God are arguments about the thing itself. Only horror accepts good and evil going in.