One key cause of piracy left out of this analysis is the significant demographic of people who have internet but can't buy things over it. This usually describes teenagers in developed countries who have internet access, but don't have capital that they can freely spend on digitally purchased objects. The amount of young adults who actually have jobs is really falling in developed countries because of the promotion of internships and volunteering opportunities, which are easier to obtain than jobs and have equal or greater prestige. Even if they do have income, they may not possess credit cards. There's a good portion of this group that can't even drive to purchase things with cash. So every new possession they obtain by spending money, or rather getting an adult to spend/provide/transfer money, is a significant expenditure.

In this situation, knowledge becomes something it seems irrational to pay for, because it seems like it "should" be liberated. They might acknowledge that being able to understand physics better or win arguments has a value of $20 or $50, but they won't spend that when they could get a comparable result with an expenditure of time, even if said time is worth more than the money would be.