Comment by Ekaros

Also when I think of better end of non-fiction. How many books on certain topic I need? Say ornithology or on birds... Maybe a few at best. Unless I am collector or interested in that specific niche. Which already massively cuts down audience. Take history. Huge overall. But if you only go for specific events, periods or areas(town for example) it might cut down audience significantly.

So I think it is fair to say for fiction that some niches could be lot smaller say than generic fantasy, romance and such. And also I can read lot more fantasy books if I get around to it... Some of them are bloody enormous series too.