(as author of original post)
Agreed. But GitHub did a lot more than just that - across the board it removed the barriers to collaboration (I used to run a few projects on SourceForge, and contribute to others; the ease of GitHub was like a breath of fresh air).
It got people excited and feeling free and able to collaborate.
...and so (I suspect) we're today less tolerant of unexpected barriers to collaboration. GitHub gets you hooked, then makes it extremely difficult to manage the "handover" part of a project (something that SF - for all its failings - handled pretty well).
The projects that die this way may well never have existed without GitHub in the first place - but that's not an excuse to just kill them off under a burden of maintenance crud.