I'm an advanced user myself and I use many different operating systems, including Linux and OSX, however I'm not talking about myself in this post... I'm talking about the many normal users out there that use only Windows and believe me there are a lot of these. Now, regarding myself... I'm not a professional developer or a programmer, even though I know a bit of programming and for my kind of work I actually need to use mainly Windows.
You cannot look at things only from a developer's perspective or a programmer's, especially if you want everyone to be able to use your product or service fully and you are targeting the mainstream market... it needs to be easy and accessible. For that Windows support is a must have, regardless if you like it or not. What if somebody told you need to use Linux in order to be able to be on Facebook for example?
But you don't need to use linux to be on Steemit, far from it, right?
Also, I did just check the codebase and there's build compatiblity fixes for VisualStudio in it.
BTW, just to be balanced: I, too run multiple OSes, mostly because I have to in order to get things done in a timely fashion.