Not that I disagree with this, but that goes almost directly against "Mak[ing] that source public via GitHub or another favorite long-lived, erosion-resistant host. Git’s portable, so copy or move repositories as you go."
Any self-hosted service or solution is going to not be erosion-resistant by virtue of not being for-profit.
Of course the end-result is easy to move out but the build pipeline is more dependent on GH.
Not that it matters but it could be cool too to pipe SSG's output through a managed VPS just to show you don't need Github to host your static files.
And for-profit services are? Often enough it's the VCs which ruin a service by pressing out money before it inevitably dies because the experience has been degraded to an extreme degree.
[0] Also, thanksnotreally for cherry-picking and putting words in my mouth with your use of `!M$`, screw you too.
Personally, I have a different take than the OP, although I'm not sure this is really a disagreement. I would argue open data formats are more important in this context. If I write text in Markdown, it doesn't matter whether I'm using Emacs or a closed-source, proprietary commercial editor; the text isn't tied in any meaningful way to the editor. Likewise, a Git repository hosted on GitHub isn't tied in any meaningful way to GitHub. It's... a git repo.
As long as GitHub isn't doing anything that I particularly object to -- and "oh woe, it is owned by Microsoft" is not an objection I share -- there's a pretty good case for continuing to use it. I'm taking a calculated risk that it's both unlikely to go away anytime soon and to markedly change business direction in an unfriendly way, but if it does? As long as my local copy is up to date, I can re-publish it anywhere and just, well, stop using GitHub.