Chevrolet sold 182,857 Malibu sedans in 2017 in the US.
Subaru sold 188,886 Outback Wagons and 49,837 Legacy Sedans. That's nearly 240,000 mid sized cars with fewer dealerships than Chevrolet.
Why wouldn't Chevrolet maximize the appeal of their Malibu by offering all wheel drive? Or different body styles such as a wagon or coupe? Or a real "sport" model? Can they afford to turn away buyers that may be looking for an all wheel drive sports sedan or a "tall wagon" like the Outback (especially when they intend to base many different vehicles on the same chassis in the future anyways)?
It's not like these are entirely different models. They are simply different variants of a car that they were already going to offer anyway. Would it not benefit Chevrolet's customers and their dealerships to offer more variants of existing models? Why do they target the Toyota Camry sedan exclusively when they can do that AND create a niche for themselves in other sub markets where Toyota does not compete?
I ask the same questions of Ford with their Fusion. The sedan market is shrinking, but it is still huge. It would benefit both companies to stake a claim to a more diverse range of market segments with the same model (coupe, "tall wagon", sports sedan, etc.). They both have the basic sedan and hybrid sedan covered. Ford at least offers all wheel drive. Neither offer station wagons or coupes.