Look I was astonished a few years ago to discover that Christian fiction is a massive genre. Yes. There are whole publishing houses who specialise in love stories, detective stories, action/spy stories, even westerns which are written on specifically Christian themes and aimed at born again and fundamentalist Christian audiences. It's massive. A multimillion dollar industry. Especially in the US.
The thing with pagan fiction is that it slots so beautifully into the well established and eclectic "Fantasy Genre" that it sells far better and to a wider audience than just its faith base. But fiction based on religious doctrines and traditions in not new (Heard of The Pilgrim's Progress, anyone?)and is far from being limited to paganism. I know for a fact there are Islamic publishers who specifically market books to Islamic audiences. Isaac Bashevis Singer, until long after he began publishing, was considered primarily a Jewish writer for Jewish audiences. Mary McCarthy gave voice to Irish Catholicism.
It's hardly a flaw in Wicca or paganism, if Druids, dragons and damsels in distress are memes which have a great deal of cross cultural appeal.