All of the comments so far are about the author’s cut. This is the second book he’s written, with the same situation. Clearly it’s worth it to him. You should just consider it a hobby project, and he’s giving readers the option to get a full color print copy of the book.
The first book, Game Engine Black Book Wolfenstein 3D is fantastic. This goes back to an era where one person can read the source code for a game and understand what it actually is doing at the hardware level. It would be fantastic for an entry level computer science class or someone who just wants to understand how a game engine works. The exhaustive color illustrations and images, the reason why the author makes no money, make is so much easier to grasp the concepts. If you are an experienced developer or someone who can understand complex topics just by reading text and formulas, the this isn’t such a big deal.
Can’t wait to read this new book.