Why does gmc name their models different than chevys?

the chevy colorado is the gmc canyon, the silverado is the sierra the express is the savanna. i just dont understand the difference between chevy and gmc besides the fact that gmc only makes trucksWhy does gmc name their models different than chevys?
The difference is the GMC is classier and looks nicer. Different Grilles, interiors, tail lights...the GMC is nicer. Different brands. The others differences:



GMC is more expensive. It has more padding in the walls %26amp; doors and such, making it a quieter ride.



There are so many differences....Why does gmc name their models different than chevys?
There are differences like the option available, interior, different grills, chrome bumpers, gmc logo, etc... If they were exactly alike then you have a point, but they are not exactly alike.