...this is a github repo. Pointing to an open source project. That is not forced to use any vendor-specific systems to function.

It's a pattern that occurs in commercial software yes, but Open Source has its own version of building mirror ecosystems. Collaborating to bleeding edge issues on robust infrastructure is very hard, so junior engineers that want to collaborate in open source (often for reputation building) can do so in these mirror ecosystems, it's an added bonus if they believe that they are contributing to the bleeding edge instead of rebuilding an enantiomer tech stack.

The author is Brad Fitzpatrick.

He worked at Google for 12+ years. He created memcached, WebSub (PubSubHubbub), OpenID, and Perkeep (Camlistore). He's a late-stage co-founder of Tailscale.

If he's a junior engineer, then I have no idea what a senior engineer is.