With books, the time commitment you need from people for them to "try" what you created is immense compared to other efforts. Like if you are a painter, it takes a couple seconds for someone to have a look at what you created. If you are a musician, a few minutes spent on a track is enough. For a book, you need someone to sacrifice a few hours of their life for a non-guaranteed return, time they could spend reading something that they are practically guaranteed to enjoy. I don't write fiction, and don't read it, but I imagine it must be very hard for someone creating works of that sort.