Protection class is a real number on your policy
Carriers rate the distance from your front door to a responding fire station and to a usable water supply, expressed as a protection class. Crossing a threshold between classes can change a premium noticeably, and in a city that keeps extending into open desert, two houses a few miles apart can sit in different ones.
Ownership this high concentrates the exposure
With most households owning rather than renting, the family balance sheet here is largely one address. That makes the dwelling limit and the liability limit the two numbers worth getting right, and both are usually set once and never revisited.
Open desert drains onto new development
Ground that has never been built on sheds water quickly, and new roads and pads change where it goes. Flood is excluded from every homeowners policy sold in Arizona, and in a city expanding into undeveloped land the maps are often behind the construction.