Most book authors simply don't make money from books. Especially if it's a technical book.

Unless the billing system tells you explicitly "you see the lack of people here compared to last month/year/some other time period? well, we actually possess the technology to find out who these potential people would have been, so we reached out to them and asked if they were going to buy your book. they all said 'yes, but not anymore, since I can now pirate it' and that's why your book stopped selling as well as before", how can you be sure you were going to make that money?