There are probably millions of works of art (books, music, videos, games, etc.) on hundreds of thousands of fan websites out there with all this and more and V/P/C hasn't shut them down. If protecting IP is so important then why don't all fan sites suffer the same fate with a C&D and disappear within 30 days? What makes certain projects a specific target?
IIRC, Stage 9 was said to have been shut down because STO was planning a release of similar walk-throughs. Axanar got squashed for obvious reasons delineate numerous times here and elsewhere. There's cause and effect and there's always a reason.
What made this book project a target? Was it simply the usage of screen captures from canonical sources? Were they making money off the venture, or is this simply just some random occurrence to make an example of someone for all the world to see? The final option I find to be least likely. There's usually a reason that is publicly quantified somewhere.