Because it's further away. And lots of older applications (e.g. vim) were designed when most keyboards had the escape key placed in the same spot where the caps lock key is today.

And some Macs don't even have an escape key.

I personally like to remap caps lock to control or use a keyboard that has that layout by default. I never use caps lock and it makes control-based shortcuts more ergonomic.

I use it as both. Control when held and escape when tapped.

setxkbmap -option ctrl:nocaps

xcape -e 'Control_L=Escape'