Eh,
GM had too many damn divisions before.
Yes, I liked Pontiac but fact is they (GM) were spread too thin and for a long time they had multiples of the same damn vehicles with very minor differences. I still have no idea why there are GMC trucks and Chevy trucks.
GMC started as a way for Buick and GM dealers to sell trucks without sullying their lots with plebeian Chevys. That those dealers are still around could be part of why GMC survived.
My understanding the main reason is that the 'professional grade' and other advertizing was too good. A survey had 20% of GMC owners switching to Ford over Chevy. Without some strong reason to keep it, the feds would have had GM ax GMC.
Careful there. Who do think is responsible for the Sonic? Though they felt a need to change the name to GM Korea....dumping the bad ones (cough cough Daewoo manufacturing)...