I don't know why people assume that the siren systems local governments install aren't the affordable option...
What do you think is cheaper and provides the most safety....a single siren loud enough to cover a very wide area, or the state reimbursing hundreds of people to buy inadequately installed and tested sirens all over the place?
I can guarantee that if you had everyone install their own systems a significant portion would not be installed correctly, and another significant portion wouldn't have the needed maintenance performed to maintain reliability.
I guess people don't understand the innate cost effectiveness of consolidation at scale?