If I want to support Windows I have to setup a (virtual) machine with a license code just to have any basic functionality. As someone who doesn't work with Windows anywhere, this is a huge hurdle. Then there's the hoops I'd have to jump through just to get a decent shell and a compiler ready.
Oh, but the fun doesn't end there. Which version of Windows are we talking about? More than one? Ah, well, each of these will require its own machine (virtual or otherwise). With matching keys, of course.
Supporting Windows is a pain and when it's not required for what I want to do, I'm simply not going to do it. Period. I have better things to do with my time.
Letting people who want this code running on Windows do it themselves and having them submit patches upstream is a perfectly valid choice.