Well, the main thing is, that you like writing. Regardless of how many people buy the books. As long as you write because its your "thing", everything is ok. I mean, you don't have to sell books to get some food on the table, do you.
So all what happens on the writing side is kind of a bonus.
May be you also have picked (well, you didn't by choice perhaps) a bad time to become a writer. To sell your romantic novels as traditional paper books may get increasingly difficult, in the times of e-books. In the fact book segment it still is different, if you have the right subject.
There is a YouTuber called Ian McCollum (aka Gun Jesus) who just published a book with great success. Its called - wait for it - "Berthier to Famas - French Army Rifles from 1860 to Present Day". Talking about niche markets...
Its a big hard cover book that costs $85 or so, and yet its almost sold out right at its publishing date. But that is still a book that people put on their shelve, with lots of photos and drawings and all. As a e-book that would be much less appealing and also harder to use as a reference book.
But such books are less "writer friendly", of course. There is not much so room for imagination and artistic freedom, even if the facts are wrapped into a entertaining surrounding, like your book on Indiana.