Because what they do isn't drifting, its powersliding. The difference is a feat of braking, as apposed to a feat of throttle. I can drift an FWD car, yet cant maintain it.
Drifting is not a sport. Judged like figure skating, its an abomination. What is a drift? Its a way to avoid spinning the car and losing too much lap time when racing. Its a way to get through a gravel or snow turn fast without letting the engine revs drop. Drifting a car is fun, but it is not a sport.
After many winters of rwd cars, it is second nature. I've drifted the entire course at mid ohio, it was fun, but is not a means to any end.
If you want to make drifting a sport, here is the formula:
GT series, stock based cars.
RWD only
Max weight of 2500 lbs
Min rwtq of 300 lb ft
Locked rear end
Spec tire, super hard.
YOPu set it up so the cars dont get traction, therefore correction by counter steering, AKA drifting, is a neccesity.