Exactly. Your post answers OP's question. The root cause of the SDK fragmentation is because Microsoft sees diminishing returns for Windows. After Silverlight

Exactly. Your post answers OP's question. The root cause of the SDK fragmentation is because Microsoft sees diminishing returns for Windows. After Silverlight failed to gain adoption, they started losing interest in the desktop. When Windows Phone was killed, there was even less interest in UWP. It's a shame because .NET is quite nice.