Someone will have to answer this question for me. From a business standpoint: Why the book?
It seems to me the book should be the final stage of any literary campaign-- the culmination-- not its beginning.
In the first months of World War II, the "jewels of the fleet" in navies around the world were the battleships. They turned out to be obsolete in that role, in that they were lumbering, expensive, and needed supporting infrastructure in the form of protection. They were shown to be extremely vulnerable to small, quick-strike planes launched from land or by aircraft carriers.
The ULA was successful when it attacked established literature's weak points, not its strengths.
One thing the publishing industry can still do is put out there millions of books with a huge supporting infrastructure.
Writers, however, are wedded to the idea of the book.