We (can I say we? I don't work on Windows stack stuff at here but whatever) are actually one of the biggest open source contributors in the .NET world, granted that's just my opinion and I don't have data behind it, but here's a list of things we've open sourced: http://blog.stackoverflow.com/2012/02/stack-exchange-open-so...
MiniProfiler is my favorite one, and now exists in .NET, Ruby and Node.js due to my insanely smart co-workers.
Please don't take it as a criticism of your work - but the fact that one small company (<100?) that does OSS as a side effect (plus recruitment retention effort) can be one of the largest OSS contributors in the dotnet ecosystem says its not a vibrant and thriving ecosystem.
SE has a very high reputation as far as I can tell so its not a quality issue - it is in this case a problem of quantity.
As someone commented the idea is to focus on Azure and mobile - but that is no substitute for lots and lots of developers in a culture of releasing stuff outside their immediate company and so driving each other to new heights
The snowball has been growing here for the last few years. The .NET community was historically not very "open" ... but ever since nuget and github, attitudes have definitely been improving.
MiniProfiler is my favorite one, and now exists in .NET, Ruby and Node.js due to my insanely smart co-workers.