It sounds like what happens in every other instance of engineering: trade-offs. Emphasise performance in one metric -- preventing roof collapse and preserving the integrity of the passenger compartment in this case -- and it can come at the cost of other metrics (here, visibility). I don't think vehicle engineers are deliberately making cars hard to see out of, but I do think it's possible that those setting the policy which drives A-pillar thickness don't realize such is making cars less safe from a visibility perspective.
Manufacturers are more likely to be liable if you roll your car and the roof caves in, killing you.
Manufacturers are less likely to be found liable if you couldn't see through your A-pillar and hit a cyclist, as apparently proven by the article.
It's very hard to point the finger at the driver for their roof caving in, there's nothing the driver can do to stop that from happening. But there's plenty a driver could do to avoid trouble from blindspots.
