Correct me if I'm wrong again, I don't think the drones 'fell' from the sky, more so lost connection and went into automatic land mode, which is the safety feature if they don't know what else to do, or run low on battery. Unfortunately for the drones in Perth and Melbourne they were over water at the time. I doubt drone displays directly over crowds would be allowed anyway, in the same manner fireworks are not. So I do not think there is much of a safety issue at play.