Also those authors need money from somewhere so they might not have done well themselves. I feel people recommend financial books just so others get used to reading quite a bit... For the authors that do manage passive income - or anyone for that matter - they did it in a safe(ish) reproducible way. Investing in bitcoin is like going to a company in silicon valley, listening to a talk and deciding to provide capital - both are similarly risky and if you say the likelihood of bitcoin of other currencies being suggested to you is similar then you might well be drawn in the wrong direction...
Bitcoin's still a speculative asset though.
Bitcoin is to good to be true that's why it scares the shit of me ...