"... ideally you're supposed to be famous so people will buy your book."
Not true. Not even ideally. More often, publishers want writers who know their subjects and can turn in a good manuscript on time. By way of illustration: Over 20 years ago I wrote a book titled The Modem Reference (long out of print). I was merely a midlist science fiction writer at the time, and wasn't famous for anything public. But the book sold 200,000 copies.
If I wasn't famous, why did it sell so well? Because I brought the required knowledge to the book, and I wrote the book in an appealing, easy-to-understand style. When I started CROSLEY, a New York Times bestseller that also made the WSJ and Business Week bestseller lists, I brought only my style and technique, over five years of research, and enthusiasm to the book. I'm not known as a great biographer or historian, but since December, 2006, the book has sold more than 48,000 copies in hardcover.
Here again, I was not dealing with a subject area in which I was famous.
Point 1 of 2: The right knowledge, a good presentation, and great writing can sell books to the public--often more effectively than fame. And in the end publishers are out to sell books, not to link to fame, unless it's move-star level fame. (Not incidentally, as an editor I negotiated the deal for three of modern science fiction's bestselling novels ... written by an author who was a complete unknown at the time. Of course once that author became famous within the SF field, fame did help sell books.)
At the same time, there are books by famous authors that go nowhere. Whether they flop because the author tried something new that didn't work, or because she lost her writing ability, or because she's only writing the same story over and over doesn't matter. That kind of fame doesn't automatically sell books. (At the same time, there are bad books by famous authors that do well. Why? See my post on why and how bad books get into print.)
Books by and about famous people can flop. Examples: Spiro Agnew's suspense novel, and lots of other rock and country music autobiographies that didn't become million-sellers.
All of which leads to Point 2 of 2: Fame alone doesn't make a saleable book; the aforementioned enthusiasm and good writing are usually necessary. (Point 2.1: Bad books get into print and sometimes do well for reasons that have nothing to do with fame or quality. There's an exception to everything, even gravity.)
Copyright © 2007, Michael A. Banks