OEM brake lines used to be terne coated. I think they switched to an organic coating to get the lead out of cars.
Copper and nickel are very expensive. I too think cars in the rust belt should be made of these materials, but the manufacturing facilities haves no way of knowing where cars will ultimately be sold.
I also qustion whether the Cunifer brake line, or other copper-nickel brake lines have the same burst resistance as the bundy tubing that is used in brake lines.