One of the main reasons for self-publishing is to cater to a niche market. Niche markets come in various forms but one that is often overlooked is the waning market. Reading fashions change, but an genre that has been great within one's lifetime is likely to still have some ardent devotees (assuming there has not been some kind of genre-specific virus or conspiracies of stealth assassins). Thus while some genres are taking up less and less shelf space like Westerns they still have enthusiastic (and frustrated) readers. Other example might be sub-genres like historically accurate romance, sweeping sagas or gothic suspense.
Another example would be classic horror (as opposed to romance in a Halloween costume). Most mainstream bookstores had a dedicated horror section only a few years a go but have now discarded the genre altogether. Even as a person who was no much given to reader horror I do fins myself pining for it at this time of year. I mean a story that, for the sensitive and imaginative reader, can summon up a feeling of true, genuine horror. Now it seems unfashionable to be horrified. Disgusted, fine--scared, okay--morbidly fascinated or even perversely turned on--totally acceptable. But the modern reader is not, apparently, meant to be susceptible to true horror.
I am not, however, really a modern reader. So do send in your horror for our Halloween review feature. Submissions are open for two more days :)