Because at least for your parent’s generation, it was also a general, “get off the streets, get away from windows, find a radio and find out what the hell is going on!” siren. Very good for alerting a whole populous that some shit had hit the fan and not to just go about life without figuring out what you were supposed to be avoiding. Very good for atom bombs, terrorist attacks, or natural disasters. Shoring up the northeast tip of Tornado Alley, we here in Minneapolis still have civil defense sirens go off the first Wednesday of every month (although most people my age think they are called “the Tornado alarms”).