If the truck has to come back after making deliveries it's usually better to load it up with scrap metal than to send it back empty.

It's a pretty damn good example of the market solving a problem by itself.

This only really falls apart when the cost of new stuff is less than the cost of recycling. High wages are not good for recycling/repair businesses.

When you get new tires on your car most places will take the old ones for free. They get recycled into filler for lower quality rubbers (you can't re-vulcanize rubber, it's like un-baking a cake)