Also let's not assume everyone in HN necessarily has money and comes from a wealthy country, in my country $22 is quite a bit to consider spending on a book, some developers earn well but others do not, or might not have a software job yet, if you are a student for example that might be 1/2 or 1/3 of your monthly budget.

For me paying something in dollars is not an option, because I don't have dollars and I have no way to buy them with my country's currency. Most people in the world are like me. Something americans and europeans don't realize

It's the relative difference that bothers people.

It's the mental friction of any payment versus no payment.

Multiplied by the risk I won't actually have time to read it.