You’ve dropped your phone and the screen shattered. Now you’re facing a costly repair until you can get a new phone. Swapping out one piece of glass or a button doesn’t seem like it should be that expensive. Why does it cost so much to fix your stuff?
I imagine, machines like smartphones are often integrated to the point of requiring almost no human labor during production. So they’re cheap. Repairing them, however, requires human labor, so it’s expensive.