What Makes a Book Popular?

What factors contribute to a book’s popularity? My data is from Kaggle, a data science resource, consisting of books from around 500 BC until 2016 and their publishing details. I seek to understand what book characteristics relate to book popularity. By modeling the genre (fiction or nonfiction) as a linear function, I found that fiction books tend to be more more popular. They are estimated to sell, on average, around 600 more units than nonfiction books.