Generating books instead of spam emails looks more professional so gullible people, who meanwhile (hopefully) did learn that the Nigerian prince isn't a prince, will buy such books (it's written in a book, and book writing is real work you know, so it must be true) to learn about all those fancy new concepts they hear about.
It's actually not that different from all these ads you see, especially if you actually watch recent youtube ads. Due to the current "energy crisis" and the upcoming winter, I've seen videos advertising magical electric heaters, which will "recycle" 85% of the energy used for heating and thus will save you lots of money. It's simple physics that warm air coming out at the front of such a device will be sucked in at its back again, but there's nothing to "recycle" here, to somehow save energy.
BTW, anybody interested in my upcoming book on quantum heating? Quantum heating will even earn you money, because it will generate certain energy efficient by-products which you can sell at your favourite online retailer ;-)