Have you seen a tear down of the authentic chargers? There's a lot going on in there.
http://www.righto.com/2015/11/macbook-charger-teardown-surpr...
The author also does consider the cost of the components.
They could also sell replacement user swappable magsafe cords and defang many of the complaints. But then they couldn't effectively charge $90 for a replacement cord.
I have wondered if the degradation of the cord wasn't some sort of safety guarantee rather than planned obsolescence. When the cord wears out you buy a new one instead of using the ancient one from eight years ago.