One thing you missed is that there just isn't the same culture around open source development in the windows world. After all, why should someone devote their time to make windows (a commercial, closed source product) better?
OTOH, here is how I got involved with this. I was developing a file system on OSX that I then ported to Linux. When I looked to port it to Windows I did not find any satisfying solutions and I ended up writing WinFsp.
Why port to Windows? Because it still has the biggest market share and because it was an interesting technical problem.