Did some more research:

From github's site:

GitHub Pages Basics / Securing your GitHub Pages site with HTTPS
Securing your GitHub Pages site with HTTPS

You can enforce HTTPS to add a layer of encryption for traffic to your GitHub Pages site if it has a github.io domain.

With HTTPS enforcement enabled, HTTP requests to your GitHub Pages site will be transparently redirected to HTTPS.

HTTPS enforcement is required for GitHub Pages sites created after June 15, 2016 and using a github.io domain. If you created your GitHub Pages site before June 15, 2016, you can manually enable HTTPS enforcement. HTTPS is not supported for GitHub Pages using custom domains.
https://help.github.com/articles/sec...te-with-https/

So yes, the current method has been broken for 2 years.