That means that rightsholders can expect at least $3,000 per title (less costs and fees), which will be shared among the rightsholders for that title (if there is more than one rightsholder)
if there is more than one rightsholder
Again, a publisher will have a whole catalog of books / titles, a non-negligible portion of that the publisher will own the copyright to (no one to split it with). There's all kinds of books outside of novels, there's media tie-ins, IP franchise books (ie Star Wars), childrens books, textbooks / reference materials, etc etc etc. Yes, with novels the author tends to own the copyright, but you're forgetting all of the other kinds of books out there.