Microsoft has never understood open source. This is why they bought GitHub and npm, and paid Docker to make it work on Windows, and why GitHub and the most important parts of VS Code are proprietary software.
They use open source as a marketing buzzword, not as a philosophy, and it shows.
I think perhaps TypeScript is the only counterexample.
I think they understand open source (and show it by many projects) but like you said, it is not their core philosophy.
They are a proprietary software and cloud vendor super house. They are very successful like that. Open Source is 3-4 level down to their main strategy.
They use open source as a marketing buzzword, not as a philosophy, and it shows.
I think perhaps TypeScript is the only counterexample.