Okay yes, but it probably isn't going to be down for more than a few hours at a time. I'm sure pull requests and issues can wait a few hours vs. actually fixing bugs or writing new code. Right?
PITB, yes. But you can still get work done.
Plus you are forgetting that lot of automated jobs get triggered on github changes. Many shops kick off all kinds of tests, deployments, and other things based on changes to the github repo.
My point was simply that you can still be productive when github goes down, if you want to be.
I don't think you're "wrong" for the developer use case, but the reality is that it can bring large teams to a screeching halt.