Actually you can search and learn about cryptocurrency online.
Why bother to pay when you can do it for free. lol
Just think about the author over 2 or 3 years with (hmm, let's say, over 500,000 books sold at £20/book).
Now do the math
To be honest, I have sold about 40 in 2 months (£4/$6 royality for each). I wrote the book as a historical reference of popular coins chosen by the community one year ago.
I am helping to promote cryptocurrency to a wider audience.