Bombardier effectively went broke trying to break into the the low-end of the Boeing-Airbus market with the CSeries, no?

I found that odd because, as you say, they certainly have the expertise and track record for seemingly comparable projects. To provide evidence for the hypothesis (which is a larger theme in political economics) it would be interesting to see what the precise engineering and management hurdles were as compared to smaller aircraft, especially the marginal cost. The crux of the hypothesis would be that techniques needed to remain competitive in Boeing's market--e.g. foldable wings--would be regulated in a way that made them especially costly to develop and gain regulatory approval.