It is free and robust, and there is not much bad Microsoft can do to you. Because it is standard git, there is no lockdown. If they make a decision you don't like, migrating is just a git clone. As for the "training copilot" part, it is public, it doesn't change anything that Microsoft hosts the project on their own servers, they can just get the source like anyone else, they probably already do.
Why not Codeberg? I don't know, maybe bandwidth, but if that's standard git, making a mirror on Codeberg should be trivial.
That's why git is awesome. The central repository is just a convention. Technically, there is no difference between the original and the clone. You don't even need to be online to collaborate, as long as you have a way to exchange files.