Recently I've corresponded with several knowledgeable authors who were vacillating between self publishing and signing a(nother) trade contract. They were all fully cognizant of the trade-offs involved in trade authoring, and were trying to decide whether or not to go the self publishing route for a particular title. I'm stressing "particular title" because it's important to note that self publishing and trade publishing coexist. In some instances, a self published title will sold to a trade publisher, in other instances, the author may write both for trades and for self publication.
I can, and have, made all sorts of arguments as to why self publishing will often result in a higher pay day for a work-a-day nonfiction writer. But the main attraction of self publishing for me is being the boss. Self publishing means retaining the right to do whatever I want with my work, including licensing it, packaging it in different versions of books that may include other contributors, or simply selling out down the road. Authors who are confronted with the decision of whether or not to sign a trade contract end up concentrating on the terms they have a chance of altering: royalties, advances, foreign rights, editorial input, non-compete and out of print clauses. The forest that gets missed for the trees is giving up ownership of the work.
That loss of control doesn't mean much to authors who have no publishing ambitions of their own and who are willing to accept that the trade publisher will manage the title with the best interests of the author at heart. But it doesn't always work that way. Correction, it doesn't usually work that way. The reasons are myriad, from young and inexperienced staff at trade publishers not being good at their jobs to old and experienced staff being wrong or stubborn. The interests of the publisher and the author can simply diverge due to other titles in the publisher's list that compete with the author's or require more attention due to higher initial investments, or due to restructuring and changes in the business plan that come and go as often as editors. To an author with one title in print, the decision to sell into a major retailer at a deep discount for branding purposes or to redesign the book to fit a series can have a major impact on the sales and on integrity of the work. For the publisher with hundreds or thousands of titles in print, what the affect will be on one author isn't even a consideration.
I'm currently trying to decide what to do with a healthy chunk of a new book that's in the draft stage and drawing enthusiastic visitors online. I may publish it, with additions of my own, as a companion to another book of mine. I may work with another author to create a more comprehensive work with a much higher cover price. I may try to license the work to the trade publisher with the leading book in the genre, or I may do all three. Self publishing means that I don't have to give up on the work after the first publication, or wait for a trade publisher to decide on a new edition (and what their marketing people want to see inside). Self publishing means that I'll never have to watch one of my books die a lingering death because of decisions made by an apparatchik at a trade publisher.