They just went by gut feeling. Classic snake oil marketing haha. No real data to back things up, just let some famous people say they feel better when using it.
Personally, I run my own Forgejo instance for the private repos I actually care about. But it's basically impossible to not have a GitHub account right now. I use "Refined GitHub" to make the UI somewhat usable.
As an isolated event, this is not great, but when you see the stagnation (if not downwards trajectory) of GitHub as a whole, it‘s even worse in my opinion.
edit: Before someone says something. I do understand that the underlying issue is some issue with Azure.
I believe this is the reason why we can even have this debate. Without this kind of competition we would not have these subsidies.