Does one need to serve every category?

More and more car manufacturers are entering SUV and Minivan categories……highly profitable they are. Chevrolet, Buick, Pontiac, GMC, Saturn, SAAB, Cadillac - all GM US brands offer multiple choices in SUV and Minivan categories. I wonder if GM could have benefited by a couple of brands serving these categories, instead of all competing.

Even Porsche could not resist……..