Earlier quoted context omitted.
It went un-noticed here, I think, but The Pragmatic Bookshelf recently fired most of its staff and are taking on no new books. In the email they sent to authors, they quoted a 40% YoY fall in non-fiction sales, industry-wide.
Honestly, I wonder how some of these publishers stay in business at all. I haven't written a book, but I've been a technical reviewer for friends who have been published with some of the larger technical publishers. Nobody was making money from the process. I do wonder if maybe they're just taking on too many titles and reaching saturation. Do we really need "The guide to making X on Y with Z" for every potential ite…
From the people I know who wrote or co-wrote books, the way you make money is in future interview processes.
I don't know if they still do it, but when I interviewed for Google, they had a self-ranking system of how competent you are in each technology, and the only way to get the top score was phrased something like "I wrote the book on it (yes, an actual book)".