I agree that scale is the bigger factor, but the infrastructure matters too: Consider invite only vs writable-by-everyone default. Open source development moved from a lot more invite based in the mid 90s to a strong writable-by-everyone social media model particularly with the adoption of Github vs svn/cvs. But the scale issue is an argument that open source should have been going in the opposite direction. More unpleasant actors means more justification for reducing participation.
I suppose the thing that changed with GitHub is that 1) issue trackers became widely available, and 2) the concept of pull requests (and "drive-by" contributions). Before that, it was basically "email me" for most smaller projects (or maybe an email list on SourceForge).
I suppose "ignore some asshole in your email" is easier, and also hard to pile on comments in a private email box. But beyond that, I'd say having an issue tracker is a net positive, as is the ability to create PRs easily.
I wouldn't say that "social media-izing" is a good way to describe any of that, but I understand what you mean.
The main problem is probably more "brigading" from Twitter/X/Mastodon/Facebook/whatnot.
There were trackers before github for sure-- but like it's a pretty ordinary setup to make issues private to project members until triaged... that sort of thing pretty much kills brigading dead and it's a thing you can't do on github.
There is a continuum between totally private and what github provides, with self hosted tools you could hit a number of different spots on that spectrum. Cynically one reason for the lack of flexibility is that the maximally permissive side is probably better for the expansion of Github's business.
