Here’s the thing about Lovecraft: He was an atheist. An adamant atheist. He believed in not one speck of the supernatural. Nothing. They also called themselves at that time, “realists”. If it could not be detected or proven, then it was likely false.
So…a truly guilty pleasure of Lovecraft’s was supernatural fiction. He loved the stuff. He reveled in it. Combined with his ironically Puritan ethics, such guilt must have driven him close to bats struggling with the incongruity of it all.
Thus, to assuage his guilt and put the matter to bed, he was struck with the spark of brilliance to create fiction in which the supernatural was given a SCIENTIFIC origin and principle.
This is the genius of Lovecraftian fiction. It puts the shade of supernatural within the realm of what is real. There is no magic, only science. There are no gods, only alien beings. Evil has no place; but cosmic indifference to squalid, tiny, insignificant Man rules the universe.
Therein lies the art of what Lovecraft did with horror/supernatural fiction. Nothing was the same after he created his literary work. It has dominated horror fiction and fantasy since the day he began to publish these works.