This is more like application logging and tracing.

At Github's scale their setup and micro services depth would necessitate some type of correlated based tracing like this.

Heck even if your architecture is 1 layer thin OpenTelementry is still useful than crawling through logs every time there's an issue.

I think you are confusing "telemetry" here. This is not about Cookies or "phoning home" or Advertizing. This is about collecting logs, metrics, traces from (Micro-)Services running inside your own DC/Cloud for operational purposes (e.g. troubleshooting incidents).