Because Windows really is shit, both in usability, and what can be done with it, and yes in the freedom RMS preaches about (I really agree with him in this).
I left Windows in 2008. Since then I use various Linux distros. I still helping out people friends, family, acquaintances with their computer stuff, and I nearly get braindick every time I have to sit 10+ minutes in front of Windows, so unusable. I converted a handful of people already to Linux (even women), and I won't stop doing that.
I don't game that much, I do more "work", and I enjoy such theoretical brain-teasers like the crap I wrote about the TES and F games. Last time I installed Skyrim, instead of playing I started to write a mod manager bash script. Then I stopped because I lost interest in Skyrim. Maybe one day I'll finish it. The script I mean.