Evacuation notices can be, and are, announced on AM radio during emergencies.

Having lived in disaster prone areas, people tend to be glued to the TV and radio before, during and after to get updates on the situation. TV and the internet are the first to go with the power, and even if you have a generator, that doesn't mean your internet connection will work. Radios will.

I don't think the OP's point was that SiriusXM was being used for emergency coordination, but the lack of a traditional radio in the car forgoes the existing emergency radio infrastructure.