Cause if something catches and pulls hard on the cord you would prefer it yank the cable out of the socket and you just plug it back in, rather than either strip the screw and ruin the socket or even pull the entire socket out of the wall. Or if you trip on that cord its much safer for you to have that cord come out and only trip you a bit than it catch, go taut, and send you falling on your face.
And guess who isn't willing to actually spend the money to get that "Lego-like precision" and will instead just blame everyone else who works for him instead.