Not everyone interested in Tor is educated enough to reinstall an OS. Or they need Windows for something else they do. Or 50 other things. Or maybe we're concerned about VPN leakage, or any other thing than tor that we might use to obfuscate traffic.
The fact that you run Windows as the OS on your computer means you are not very interested in anonymity or security. Other things are more important. like playing Fallout 4.
Not everyone interested in Tor is educated enough to reinstall an OS. Or they need Windows for something else they do. Or 50 other things. Or maybe we're concerned about VPN leakage, or any other thing than tor that we might use to obfuscate traffic.