It would have been more cost-effective to share engines between car lines like Ford did, but Chevy, Buick, Pontiac, Cadillac, Olds, and GMC all used very different engines for many years. Sometimes efficiency is trumped by brand rivalry, even in the same company. Why don't all the US military services wear the same uniforms?
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!