Quite simply because the rules are different. In the same way that Football is played with a round ball and Rugby with an oval one.
There’s nothing to stop anyone who wishes promoting a range of competitions to be shot with basic rifles and simple clothing. Good luck by the way with writing the riles and specifications. If the discipline proves popular then it could overtake and eventually supplant the current disciplines on offer. However as there seems to be little discernible demand for such a discipline I can’t see it being a success in the short to medium term at least.
BTW Have you tried shooting a 3x40 without kit?
Rutty