Well having to stretch your little finger all the way to the corner of the keyboard gets pretty annoying when you have to do it all the time, as you do with Vim. Much easier to remap another key close to the home row, and since caps-lock is so redundant, it is the obvious candidate.

So whether you map it directly to Esc or to a modifier, the parent's point stands: Vim users don't need the Esc key and are probably better off without it.