it has nothing to do with cross-platform
That's the problem. In previous versions Microsoft constantly patted themselves on the back about how cross platform dotnet core was. Now they may or may not be doing an about face on that and you have to start to wonder how committed they really are to being platform agnostic.
Microsoft doesn't need to give an in-depth explanation. All they need is some basic product differentiation. Call it something like "The Modern Development Framework For Windows" and only mention dotnet core in passing, as opposed to the "Windows development is coming to dotnet core" messaging that they've been doing. They could even go one better and blow the dust off some of Mono's Linux-y bits (like GTK support) and port that to dotnet core as the "Modern Development Framework for Linux". OK, maybe not call it "Modern" because of the UI connotations and the Windows and Linux specific products should have fairly different names to avoid confusion, but hopefully you'll see my point that the platform specific code should be highlighted as not being the same thing as the platform agnostic core product.
In some ways the mixed messaging over Windows development in dotnet core is also part of the low effort to attract outsiders. It might make perfect sense to people who are already on the platform, but if you were evaluating the platform cold it looks like there's no clear direction of where it's headed and when you combine that with Microsoft's mercurial track record it really doesn't look good.
C# might still be popular and loved, but from the outside looking in it looks really, really insular.
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