You honestly can't think of reasons people would want different things and value things differently?
There are reasons people choose an Xbox vs a Playstation, an iPhone vs an Android, a Porche vs a Toyota.
Some people want more heft or substance to their watch, want something shinier, $200 isn't much to them, think the SS looks nicer with certain bands - i.e. they care differently about style than someone with an aluminum watch does.
Do you know that there's also a ceramic version of the watch that starts at $1,299?
What about from an exercise standpoint? Do people who run/workout prefer the aluminum or stainless steel?