Consider that for some people that terrible operating system might have been the first system the have ever used, maybe as a kid.

I (an avid linux user who spends more time in the terminal than on a UI) certainly recall that my first contact with any computer with a keyboard was Windows 95. It was a complete mystery to me. The fascination that unexplainable object had on a 7 year old certainly had an effect on my life.

And guess what I remember? That grey interface with the blue title bar.

So as crappy as it might have been, as ethically unsound as the company who made it might have behaved themselves, the visual likeness of the system of my childhood tingles some old memories. And that is not even remotely odd. People can be nostalgic for literally everything, because we do not long for the old artifacts themselves, but for the feelings, friends and times we might have had when they were around.

For some of us the grey windows of Microsofts operating system have gained symbolic value beyond the aesthetical or functional qualities inherent to the system itself.