To speak only culturally (and not legally), the rationale is roughly parallel to the Federal-State relationship set out by the 10th Amendment ("The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.")

I've spent most of my life in "commonwealth" states (PA, MA, VA), which (legend has it) are founded on a similar principle: the local governments can do what they want unless the state explicitly decides it's a state-level responsibility.

It's supposed to be a bottom-up structure, where middle tiers (Counties) are more a pooling of resources for the towns than a middle-manager for the State. There's often lots of "regional councils" or associations rather than "branch offices" of state agencies you'd see in a top-down structure. There may also be a County-level government with more or less power, depending on the state and specific topic.

They often have jurisdictional lines that reflect their pooling of grant-writing resources rather than simple geographic regions (like FEMAs) [1,2]. In the absence of statewide guidelines, these organizations often set the standards (often because the state can't or won't).

That is, the intermediate jurisdiction is often a voluntary collaboration - usually among the more progressive/better-funded townships/departments - and it's often the small-town departments that don't participate in these councils that have this "leave us alone" attitude and especially lax standards.

  [1] https://www.shacog.com/SystemImages/SHACOGCommunities.png

  [2] http://www.nemlec.com/img/NEMLEC-mapcompress.png