I suspect the clunky interfaces are to blame: if the paywall was only 1 click ('confirm $0.1 purchase') instead of a long long form to fill most people would just click.
Even that is too clunky, IMO. I really liked the model that Readability tried to pioneer: pay a monthly subscription, view websites, at the end of the month, all money paid is distributed amongst publishers in proportion to views. Readability's purpose meant that 'view websites' was actually a more complicated step involving explicit user choice, but I don't see why this same model couldn't be used with a set of 'certified' publishers and a central authority. The common link could be 'publishers who reject advertising'.