A trick for author profitability: find a Venn overlap between what sells, and what you love writing: and dive into that sweet spot. Here's a handy diagram I made earlier.

If you've already published books and they aren't doing well, the first things that spring to mind as culprits are that the cover and blurb are wrong, or the book has a problem with the style or plotting. After that, it could just be that it just isn't resonating with the readers in your target niche, or that niche isn't big enough. In that case you could try writing in another genre or sub-genre.

I write in at least three genres, and love them all, and the books all seem to be well received: but it is only in my third genre that I hit the sweet spot. I'll still write books in all three genres, but now my sci-fi work subsidises books in the other two. The good thing is that finding my sweet spot on the third attempt wasn't selling out: it was still writing something I love, but I originally just didn't think I would be any good at writing sci-fi. Readers proved me wrong and gave me the confidence to continue! Also, trying something new reinvigorated me as a writer.

Peace, love, and good luck to all my fellow authors.

Where next? You might want to follow me and my work, or even buy my books. Many thanks!