They're far too heavily invested in C#, and good alternatives, like F#, are viewed as too difficult for the majority of their customer base to deal with.

They can add these features, let less ... able ... customers argue over "var" and what they'll use, while pleasing other users. C#'s seriously annoying to code in due to it's statement-oriented nature and lack of basic features.

Additionally, because libraries take dependencies on C# compiler implementation details, other languages do not interop as seamlessly as the .NET/CLR concept would have us believe. Looking at things like the precise output of lambda expressions, or all these APIs that take object, then read the properties as an argument list (which should just take a list of tuples instead).

Also, just imagine the fallout of "Microsoft abandons main .NET language!"