70 Swinger wheel size?

Let's put it this way. An A12 rr/sb (the lift-off hood cars) in 69 came with the biggest, nastiest wheel/tire combo available in 69 on a b-body, bigger even than a hemi car, so special they wrote the tire size on the underside of the trunk for assembly line personnel.
It was a G70x15, on a 15x6 wheel.
Why in the world, would Mopar put a two inch wider wheel and tire on a smaller car, with less wheel well room, and a weaker rear-end and 115 less horsepower?
Im aware of that, and probably wouldn't have started this thread had i been thinking better, and drinking less.