Wait, there's only one Windows? I could've sworn there were at least a half dozen active versions out there with features that aren't all inter-compatible ... just like Linux. They don't even look alike, and it causes fragmentation.
Why is Windows on the desktop? Applications and vendor support (bribed or otherwise) which boils down to "because it has been around longer."
The difference with Linux is you get a choice, and you get to argue, and it makes a difference. There are far more on-line posts about people who do or don't like Windows 8's interface than about systemd, but that isn't the cause of Window's sudden failure on the desktop now is it?