From “The Ten Awful Truths — and the Ten Wonderful Truths — About Book Publishing”:
7. Most books today are selling only to the authors’ and publishers’ communities. Everyone in the potential audiences for a book already knows of hundreds of interesting and useful books to read but has little time to read any. Therefore people are reading only books that their communities make important or even mandatory to read. There is no general audience for most nonfiction books, and chasing after such a mirage is usually far less effective than connecting with one’s communities.
8. Most book marketing today is done by authors, not by publishers. Publishers have managed to stay afloat in this worsening marketplace only by shifting more and more marketing responsibility to authors, to cut costs and prop up sales. In recognition of this reality, most book proposals from experienced authors now have an extensive (usually many pages) section on the authors’ marketing platform and what the authors will do to publicize and market the books. Publishers still fulfill important roles in helping craft books to succeed and making books available in sales channels, but whether the books move in those channels depends primarily on the authors.
This all seems new, but it’s not really new. It’s been apparent for years now. How many years? I don’t know, but still apparent.