This, according to U of S graduate student Thilina Bandara in a recent piece on The Conversation, is because that same system "works to prevent health disasters from occurring, while maintaining existing initiatives—such as public health inspections programs, water-quality testing and disease surveillance programs—to ensure our health."
Bandara, a PhD student in community and population health, broke down the jurisdictional responsibilities when it comes to public health, the social determinants of health (such as education and income) and the necessary steps involved with turning real life health data into policy action.