One reason that people get aftermarket wheels is size. They either want a bigger diameter wheel, or a wider wheel.

They get the bigger sized wheel so that it could accomodate a bigger (and probably most importantly a wider) tire. Bigger tire means more rubber on the road. Also most now get wheels because they are lighter. Less weight = better accelration.

But right now most folks are putting on their steelies for the winter. They don't want to ruin their nice, lightweight wheels plus some have snow tires on their steelies.