The subscription usually comes in a package and people hate to pay for something they disagree with, even if it's just one author of several, or the occassional mistake.
Might not be the main reason, just that these unsatisfied users are so vocal, idk.
In my experience with a voluntary donation only service targeted and used primarily by educated middle and upper class people, virtually no one pays if they don't have to.
Might not be the main reason, just that these unsatisfied users are so vocal, idk.