I have discovered that here down under with my late model corollas.
Cars end up in a scrap yard when they are worn out or extensively damaged. On the worn out front, most newer cars are covered by warranty and/or don't have any issues, large mechanical malfunctions are either nonexistant or taken care of. On out of warranty vehicles, the vehicle's value means large repairs are worth paying for - If I had a $12k vehicle and needed $4k worth of repairs it'd be worth it. However, a $3k vehicle needing the same $4k repair wouldn't be worth it. In addition, the old car is much more likely to need the large repair. Hence there are more older cars at the junk yard.
In terms of accident damage, when a newer car is crashed the damage usually doesn't exceed the amount of the vehicle. On a $12k car, if the damage is $11k or less, typically the car isn't written off. OTOH, the $3k vehicle only needs about $2500 worth of damage to become written off, hence older vehicles are much more likely to be written off. In OZ, written off vehicles go to auctions, where parts recyclers buy them. Hence, few new vehicles wind up in junk yards...