One thing that I hate about literature markets is that the median customer has the intelligence of a Trump voter.
Out of curiosity I checked out the reviews online of the best data compression book available on the market right now (K. Sayood's) - it's about 100€ for a brand new copy at 800 pages. Reviews? Sorry, one star. Too expensive.

I could understand if the price tag of 200€ was too expensive. But 100€ for a book this big, really? An A4 page costs ~0.05€ to print; do some math in your head to notice how the author makes 0.07€ per page on this book (and probably even less if you add the publisher tax). Seriously, /that/ is too much? Most people don't understand two things: writing books incurs a non-linear cost. It's actually closer to being quadratic. If n is your amount of pages, it takes O(n^2) time to write, review and edit it all. Second, nobody is actually capable of doing a calculation like this in their head.

The only reason why you can buy e.g. JK Rowling's hot air for a few bucks a copy is precisely because publishers did the calculation and figured out that it's going to be economically feasible to batch print it and distribute it. Now take any less popular book where the publisher didn't entirely have such an assumption. Jane Hodge's "Shadow Of A Lady" (in the non-mass-market edition) by my calculations ends up at TWICE the cost per page compared to K. Sayood's book. No reviews about it being bonkers expensive. Go figure.

TL;DR: the average person can't divide two numbers in their head & that writing long form books is a stupid idea in this wretched economy.