Those pillars that hold the roof up are safer if they're sturdy, but sturdy means wider and that obstructs the driver's field of vision a bit, and weighs more. "strong and slender" is possible, but it costs more. It all inter-relates.
(strong, narrow, cheap), pick any 2.
There does come a point where you start to appreciate what Polestar is doing on one of next years models (the Polestar 4): give up on the idea and change direction; no rear window at all, just a camera.