why are you using Windows?Because that's the system they give me to work on
I'd quit if that ever would happen to me. I've never taken, and will never take, a job that involves "do this task on an OS I tell you to, and you don't know".
It's unlikely to happen in my current gig though. All production machines (1000+) run some form of Unix† and for dev machines, they just give us the choice of hardware (x86 or apple), and freedom to run whatever we like. (So we have devs running MacOS, Windows, a bunch of Linux distros, a few BSD boxes, and one guy running OpenSolaris).
†We may have a few non-client facing, non-Unix systems. Like the SAP boxes. But they run bought, commercial software, not something we develop in-house. But they may run Unix as well (or something completely different) - I just do not know.