Modern cars certainly have improvements in those areas; I'm not dismissing that. Just... the engineering and tolerances didn't 'have' to be as good. The performance numbers weren't nearly as good - that afforded a lot.

They were primitive, and if the manufacturer chose it to be, robust as a result. The alternative was cheap.

Like the Death Star meme, every mechanical thing has a weak point. Well-designed cars put the stuff that breaks in cheap consumable parts in an easy to reach place.

That last piece can have more impact on the price of a repair than the part itself