A lot of people get success through dumb luck.

She also wrote something that felt resonant and in a manner where the flawed logic of her universe doesn't make itself readily apparent, which takes some skill.

Part of the problem in creating a canonical universe over a piece of fiction is that it takes a lot more thought to create the world and few people who can create that world can write compelling stores in said world. She wrote a compelling story. That said, a lot of writers can compelling stores that don't get the kind of press that Harry Potter did.