Starcraft - alt and ctrl are frequently used, easy slip to make in a rush. Pretty sure there was an override in the options menu specifically for preventing this.

depends on what games, in fast pace games you would have keys binded all over easily reachable by your left hand, shift/tab/ctrl/alt could all be used, that's why many gaming keyboards also come with a switch to disable the windows key as well.

I remember having this problem back in like 1998 or whenever that button became a thing. Sometimes if accidentally hit it whike DOS gaming and it would crash my game. No idea why people would want to disable it these days.

I keep pressing it accidentally and getting killed in FPS games

Same. People with small hands maybe, whose hand base is near the keyboard when hovering WASD.