Some authors writing in popular genres such as romance, mysteries, thrillers, vampires and zombies have gained a new audience through the KDP book promotion program. Other authors have not experienced the same increase in readers. Amazon sales are driven by the "Customers who bought also bought" list. Unfortunately, as soon as a book drops out of the list, sales decline and don't pick up unless the book makes enough sales to get back onto the also-bought list. Many authors have been disappointed to see the steady sales they made after the promotion evaporate.