This does lead into the other serious detriment for dotnet, open source. There is very little going on there because the majority of the community doesn't actively engage with new libraries or frameworks that don't come out of Microsoft itself. Hence, why I say it's too bad something isn't sanctioned.
It probably doesn't help that if Microsoft did deem it worth supporting something like ReactiveUI, their history shows that they would just rebuild it themselves. Effectively destroying the OSS.
Overall, Microsoft is improving. Just look at the changes they are making to support ASP.NET MVC as an open source project. They are just a lot slower than everyone else right now. Their research department might help them keep a few things ahead (like C#), but for the most part they are behind the curve.