Yes, but they work differently. Due to their decentralised nature there is not one switch they can turn to shut off their services or programmes. US companies can be ordered to stop their services for certain organisations, individuals or states
Yes - this is exactly the problem. Big Corporations, like Microsoft, the owner of Github, can shut you out. If you lose access to your E-Mail, or anything connected with your Microsoft Account (or Google Account) you will lose access to a lot of services that relie on it. And if you keep your source code with Microsoft and Microsoft only, you can lose access to it too.
Broadly speaking this tendency towards concentration and centralization is not only just going on in all aspects of society all over the West, more baffling in many ways is the fact that many of the instances of concentrating power and control is being facilitated and even perpetrated by the collective people themselves, e.g., putting all the eggs into the GitHub basket.
Regardless of why and how it’s happening, it seems extremely risky at best because all concentration of power and control tends to beget more abusive power and control.
Git is distributed. There are git mirrors everywhere and if you pulled the source code once locally you also still have it.
The problem isn't git -- which is open source -- but Github, which is Microsoft.
There are other open options for hosting git FOSS projects.
Sure, but then some may not remember how usage of the cryptographic algorithms was limited by the US government, including in Open Source software, all the way until late 90s in Central/East Europe.