Money. It has been said time and time again. GMC is a cash cow with next to no development costs. Pontiac on the other hand would have taken a bunch of money to right that ship, and it would have been low volume vehicles (think: SS Sedan, Astra VXR, small rwd 2+2 coupe, Firebird = 3.6TT, TransAM = 2014 Z/28, Holden…