What's the criteria for being considered "a maintainer of a popular open source project"? They never actually publish the criteria anywhere from what I can tell. They just say visit the subscription page and if you are eligible it should be available to you and if you see a charge then you are not eligible. I think though they should still be transparent about what their metric is for determining popular projects on GitHub; otherwise, the code that determines eligibility might be broken and no one would be able to tell. Or worse they could just be lying about it entirely.