Are we using GitHub differently? I don’t understand how the social network part of GitHub has to do with having your code discoverable and to discover.
I’ve never stumbled upon a project by browsing GitHub casually. It’s always through finding the product first and trying to find the source code. If the source code is on some other website, I’ll probably figure it out, but it’s be a new muscle. Same with making an issue or a PR. The barrier is higher but not so high that I wouldn’t complain about a bug.
If anything, I find the social tools on GitHub like PR reviews, issue management, and notifications to be terrible for their job. Perfectly fine for a 1 person project and absolutely awful for a team.