Anders Hejlsberg, a main architect on C# & TS, stated somewhere that they re-wrote the TS Compiler in Go because the syntax was the closest to how it was originally written and allowed re-writing to be easiest. He has a great write up of it somewhere on GitHub.

Microsoft is an insanely huge company. There teams seem to be able to use whatever works best for the project/team.

The old XKCD comic of org charts in big tech shows Microsoft as a bunch of people aiming guns at each other for a reason. They'll have 5 teams making 5 competing products sometimes. That's the culture I'm aware of. I'm not aware of the dogfooding culture you are suggesting.