Last month I had a request to review a new book on Visio. It had not been written and they were trying to line up some reviewers. Since it was a new book, I asked who the technical editor would be and was told they did not need one. Once the book was written, they would then decide.
I haved editted more than a dozen books on Visio and found that the technical editor was an integral part of the process. It was his job to make sure that the author was technically correct and was steering the read in the right direction and that the trip was interesting and well worth it. The reason I had started doing technical editting was because I had come across a few books and found that the technical editors, did not care about the content or really were not qualified to edit the book.
Except for one author who was a pen for hire, the authors I have worked for had a passion for Visio and appreciated the second sight a good technical editor could give.
It appears that the publisher of the book, just wanted to have a Visio title in their stable and wanted to do it as cheaply as possible. In our discussions, it came out that my MVP award, would look good on the book cover, but reviewers would just their name on the book and a free copy. So, my reputation would be used to increase their sales with no compensation. Not what I would call a great offer. In the past I have worked for free, but it was with authors I know and I believed in their passion for Visio.
I can not see it worth my time to do a good job reviewing for little or no rewards. Helping a friend is a definite reward.
John Marshall… Visio MVP Visio.MVPs.org
john Visio MVP 
I spent a few years as a computer book technical editor (30+ books) back when it paid money. It was never a big check mind you but the work was rewarding and steady. Your post isn’t surprising because I remember hearing from smaller publishers even back then who wanted me to tech edit books for just a free copy. I couldn’t reconcile a publisher making a profit off of my free work so I alway told them no. It’s been a while since I’ve worked in computer book publishing but the industry contractions I witnessed starting years ago sounds like they are still continuing from the sound of your story.