Dogs breakfast
So, rather than buy Sun with Java when they had the chance and not wanting to tackle the awkward-by-nature Oracle, Microsoft persist with this C#/.NET mess.
The libraries are already large and now they are going to get larger as the real world problems of cross platform compatibility dawns on them.
Clearly Microsoft sees Win10 as the end of the OS line and Linux has been deemed a better option despite their previous CEO slating it as the devil himself.
Meanwhile C#/.Net is a development money pit until they have their next "bright" idea.....