Well despite the evidence I guess I'm more of a casual listener than a proper fan, and sometimes I don't really pay attention to that sort of detail, i.e. if you hadn't told me I wouldn't have noticed that it is indeed her most popular and highest rated song here (and probably elsewhere). That fact that it's not on any of her albums may also have to do with it.
Could the fact that it was used for an anime explain why it's so well known? (And this why I didn't know about it?)
also thank you that's really flattering omg