Losing the entire history by starting with a dump is ridiculous. Authorship would be somewhat tricky (I suppose they could use username + email on file, but might run into issues where people don’t intend to make their email addresses public), but it’s not like it would be very hard to migrate the diff + message history to git. I guess they either don’t want to start the repo with a gazillion commits (actually that would be a good stress test for the system, but would make cloning harder for people who don’t know how to use --depth), or just don’t care?
Btw: now you need to clone the entire repository and run a dev server just to edit and preview a single page (let’s not get into super involved ways to clone only part of a git repo). You can avoid cloning by editing with GitHub’s web editor, but you can’t preview that way.