The Scrapyards may be the remnants of an older city, or, perhaps they just rose up out of some massive garbage dump. It is impossible to say for certain, unreliable as ancient records are.
What we do know is that it is growing exponentially. Seems that no matter how much gets recycled, the Scrapyards just get bigger, vast seas of junk and clutter, spreading across the surface of the world.
No wonder everyone wants to escape to space.