Isn't it a bit more subtle than that? The business issues with free users are well documented, but this is a bit different. What we're really taking about is GitHub - you don't have the same volume of low effort comments demanding features on pre-GitHub collaboration tools like making lists, IRC or even using the email address associated with commits.
I'd suggest that it's more a combination of: the volume of users that now have access to the world's most popular git hosting service is vast compared to the number of people who can usefully contribute, the ease with which maintainers can be contacted through it and the "friendly by default" stance that most maintainers take on a platform where your stars are more valuable in the real world than your CV.
I'd suggest that it's more a combination of: the volume of users that now have access to the world's most popular git hosting service is vast compared to the number of people who can usefully contribute, the ease with which maintainers can be contacted through it and the "friendly by default" stance that most maintainers take on a platform where your stars are more valuable in the real world than your CV.