The point was data pins. So that the new standard PSU's can communicate to the card how much power they can supply. Then on top of that someone figured that would it not be better if there was only a single cable.

Some optimistic engineer optimized it to the bone and it was decided that yep, it can handle 600W alright if the stars align just right and the user does not bend the cable in any way within the visual range of the card.