Here is the simple reason. I had a Mac Pro (the garbage can) and it was pretty kick ass. But it had a few issues. One is that I couldn't really upgrade it, another is that it had ATI video cards (I now need CUDA), and three was that if anything broke in it the whole thing was going to be a financial nightmare to fix.
So I spent 2.5k on a Windows desktop where no one part is terribly expensive, I get a 1TB SSD plus massive HD, I get a crazy nVidia card, I get a damn good processor, and most importantly I get Visual Studio which is hands down the best C++ IDE out there and getting better by the day.
Everything isn't smelling of roses. The machine is Ugly, installing development bits such as Qt is just that little bit harder than in a BSD based system, and I have to put up with some stupid windows/microsoft shit. (WTF was candy crush doing on a Windows Pro default installation?)
But nearly every issue that Windows had a decade ago has been dealt with; things such as speed and reliability are pretty well on par with Apple's OS. But then there are the little things that make me so much happier with my new machine. When I first got my MP 2013 I could hook up 3 HDMI monitors with no issue. Then an OS upgrade came along and limited this to 2 monitors. So I got a USB hdmi thing which got my 3rd monitor back but that little bastard uses 17% CPU much of the time and is a little weird. With my new Windows machine, I can have 4 HDMI monitors no problem and maybe 6. Plus I could always tuck in a special video card or two and get this up to 16 or more monitors if I so needed. But 3 is enough for now and thus is better than my MP 2013 with its 2.
Now I could have gone up to 6 monitors on the apple if I were able to get thunderbolt monitors but one look at the sticker price puts that idea away.
So I am not crapping on Apple and saying that Windows is the best, but for my purposes of developing apps on iOS, android, windows desktop, and Linux servers; windows completely rocks and just doesn't get in my way. Apple was getting in my way more and more. XCode is OK, but I was fighting with it more and more to get things to work such as certain libraries and whatnot. It wasn't that I couldn't get things done but that I was wasting a whole lot of time on non-productive configuration.
Once in a while I will look at someone's macbook pro with envy, but there is a good chance I will never go back to apple again. They will really need to step up their game for developers if they want me back. Telling me to choose the Swift language is not one of them.