BestBuy doesn't care if it stocks ASUS or not. It cares about sales and margins. If there's an extra dollar putting Gateway on the shelf instead of ASUS they will. And their customers won't care. "BIOS updates with TLS!" stickers aren't going to improve sales.
Buying a laptop creates a consumer not a customer relationship. I want to pay the least, the manufacturer wants to deliver the least. A few years out, shiny-low-cost will drive my next purchase more than brand loyalty.