Here's a second and obvious reason why some books are best sellers: The author has a recognized name. That's another way to say the person has become a brand. Think of people like John Grisham, Danielle Steel. Dean Koontz, or J. K. Rowling. In the previous blog post, I mentioned Debbie Macomber. It's easy to categorize her as a writer of "sweet romances" (as contrasted with sexually explicit ones).
After those writers hit the top of the best-seller lists a few times, they became brands. Whoever heard of John Grisham until after he wrote The Firm and it was made into a top-grossing film with Tom Cruise?
After that, Grisham books became automatic best sellers and the same is true with the others I've mentioned.
One editor told me bluntly that brand names sell books. "It's not easy to launch a book by a new author. People are comfortable with certain writers—and some of them are very bad writers—but readers like their stories."