One reason would be so that you can use C-h as backspace, C-i as tab and C-m as return without moving your whole hand. Of course you could map caps lock to be

One reason would be so that you can use C-h as backspace, C-i as tab and C-m as return without moving your whole hand. Of course you could map caps lock to be both ctrl and escape at the same time but C-[ is almost as good.