GM used to build two completely separate lines of V6 engines. They have their "HF" High Feature DOHC 60-degree V6 engines, and then they had their "HV" High Value" pushrod OHV 60-degree V6 engines, and then my personal favorite their 90-degree OHV "3800" V6, the old Buick block, so make that three lines. They're only building the High Feature DOHC V6 engines now, so I don't think that engine building capacity is an issue. That's a whole lot of production resources they've freed up in the last few years that they could and probably did dedicate to the DOHC V6 engines. Their larger 4-cylinders including turbocharged ones more than easily replace the OHV V6's. Their last 3.9L OHV VVT V6 was making about 240hp, and this turbocharged 4-cylinder is making a little bit more than that and a lot more torque. No need for a V6 in this car. Want 300hp, get the Impala.

Decisions like these are made years in advance. The OHV V6s were planned to be discontinued, and their turbocharged 4-cylinders were destined to take their place. If they really wanted the V6 in this car they'd simply allocate more manufacturing resources to the High Feature V6 engine line, if engine building capacity was truly the issue, but I doubt that's the case.

I work with product managers and I guarantee you they're just trying to differentiate the products and going after different segments of the market with different preferences, etc.

BTW I think the new Malibu looks pretty sweet! I think I like how it looks better than the Impala.

 

This generation of the Malibu is an international model (like the Cruze, sold in Australia, Korea, Europe AND North America). It was never designed to carry a V6, which would likely not have been a seller outside of North America.

In North America, there is the not-much-larger Impala that will not be offered elsewhere.