[fishpi]

I'm not sure that "can't afford" is the right conclusion. The amount of money a site makes off each person by showing ads is miniscule, so almost anyone could afford to pay at least as much for the content as the adverts make.

I think it's more likely that the mental overhead of choosing whether to pay for something (which is roughly constant, even for small amounts of money) adds enough friction to the process that charging small amounts never works.