A majority of them simply don’t survive.
Being wildly unique is a gamble for the author/publisher.
While it’s awesome that the author was able to find that odd niche that makes them unique, it’s hit or miss on whether or not people are going to get it. It took J.K. Rowling how long to become a hit? I don’t even remember hearing about the books until, oh, I don’t know, a couple years before the first movie came out. And then, it was one of my friends who mentioned them and was like, “Yeah, it’s a kids book, but it’s cool. Not something I’d typically read, but we’re a few books into it now and the kids have grown a lot. I like it.” But she said this with a shrug and a frowny face, so I wasn’t really sold.
In J.K. Rowlings’ case, she wrote a series of books in an age group I didn’t read. My kids did, so I might have gotten into it through them. As it was, I…well, I think I did pick them up once, but put them down because there weren’t dragons, dogs, horses, or princesses in them and my girls weren’t “into boys” yet, or even acknowledging they existed.
Ms. Rowlings’ gamble was that her type of story would most likely appeal to children. The world she created, the characters she shared, even the plot as dark as it got, was perfect for kids. Her writing style made it highly palatable.
Of course, it made it highly viable for readers–and a few non-readers–of all ages to slip into her stories as well.
But for a long time, I’m willing to bet Ms. Rowling was sweating it. What we forget is that time when she was still an unknown name and her sales really weren’t that awesome. She had to pick up speed and readers, and get people talking about Harry first. And that took time.
Genre’s are buckets where readers reside, a little like planets out in space.