This is in California.

The hand-wavy explanation is that in the late 70's when this initiative passed (Prop 13), home values were rising rapidly due to an influx of people moving to the state and higher inflation rates of the times. Many people that owned homes, including those that had purchased their homes and retired, were getting priced out of their homes on the property tax rates. There are other rationales or rationalizations depending on where you come down on it. But Prop 13 was intended to slow property tax growth while you owned the property, with assessment reset to full market value at sale time.

California - proposition 13.