Because more hackers use *nix, and target M$ instead.
Most "hackers" are script kiddies who wouldn't even know how to get a GUI shell on Linux unless the distro's installer set up their box to launch XFree86 on startup. Come on dude, it's pretty standard knowledge that like anything, most "hackers" are just a bunch of pathetic wannabes who have to rely on software written by the hardcore guys.
And you're basing this theory on what, exactly?