I am not so sure about that. .net core is the moment they opened up, making it cross platform, going against the grain of owning it as a platform.

If they see a gap in .net, which is filled in by a third party, they would have no problem qualms about implementing their own solution in .net that meets their quality requirements. And to be fair, .net delivers on that. This might anger some, but the philosophy is that it should be a batteries included one-stop shop, maybe driven by the culture of quite some ms shops that wouldn't eat anything unless ms feeds it them.

This has a consequence that the third-party ecosystem is a lot smaller, but I doubt MS regrets that. If you compare that to F#, things are quite different wrt filling in the gaps, as MS does not focus on F#. A lot of good stuff for F# comes from the community.