I heard a joke that you don't write a political book for people to read, you write it so you can go on all the talk shows to be interviewed about your book.
That is of course not a joke at all depending on the field. It's kinda like being published in prestigious papers.
While specialists and enthusiasts will enjoy and peek at the content, being recognized as someone who writes about the subject and can be presented as an expert of the field can absolutely be the main impact for the author.
