All their cars look like Tonka toys and have the build quality of a Chinese iPhone knock off
That's part of the "Check a few boxes and ship a translated owner's manual" treatment of the Western markets. Second to that is the over-regulation by environmental groups that operate by the "small cars for thee, but not for me" philosophy.
Can we just get back those Quad 4 engines? Why does a modern Ecotoc need 2.5L to produce the same power of a 2.3L Quad 4 W41 from 1990?
Making corner-cutting, granola-eating-environmentalist pleasing 4-cylinder-based cars is not the primary specialty of General Motors - especially when you see that most of them are captive imports(Spark/Aveo, Cruze, about anything Buick). The only saving grace is that GM doesn't opt to make cylinders appear through thin air (a la Ford's EcoBoost). Let GM make the larger vehicles for less, which is their specialty, and they will do well.
Personally, I'd not mind if GM decided to make Buick solely a Chinese brand, and then bring in Oldsmobile in their traditional positioning to cover the void in the US. Then find a creative way to (effectively) offer more car than what EPA's CAFE regulations would allow - perhaps by allowing US-spec imports of 4-cylinder cars to be placed on order but not generally stocked. If one were to go beyond that, lobby to have the EPA's regulations removed or curtailed.