Writing what you enjoy or writing what sells

If you've scanned the best seller lists recently, you'll find that they have been dominated by three types of books:
Books by authors who are already wildly popular, like James Patterson or J.K.Rowling (even when writing as Robert Galbraith)Books in a popular series, especially if that series is tied to a movie release, such as Divergent or City of BonesRomance booksIf you're an unknown author like me who's writing a new book, there's nothing you can really do so that your book falls in the fi...