Sure, but satellites do cluster in useful orbits — it’s not some uniform distribution over the space. That significantly increases the chance of direct collisio

Sure, but satellites do cluster in useful orbits — it’s not some uniform distribution over the space. That significantly increases the chance of direct collision, which has already managed to occur a few times, despite back-of-the-envelope low odds. And the risk of a runaway effect is fairly unique to the orbital setting. If cars magically kept careening down the highway after a collision, constantly tumbling and shedding parts and disintegrating without losing any kinetic energy, we probably couldn’t tolerate the current density of vehicles on roads.