For me the key element of a wiki is that anyone can modify it and the changes show up instantly without pre-emptive gatekeeping. In this case it looks like contributing requires getting a PR approved by the maintainer on GitHub. If GitHub were just the UI for submitting changes I think that could actually be quite effective as a lightweight wiki solution, so long as people's changes are deployed right away and don't…
Having no kind of gatekeeping or moderation whatsoever before changes are published seems like a fantasy of another age. Nowadays, the wiki would be co-opted by some type of spam or malicious activity basically instantly.
"Speak friend, and enter."