Why do I have to pay more taxes than my neighbor whose house is newer and larger than mine?

The most likely reason is that under California’s unique “Proposition 13” property tax system, the maximum assessment on real property is limited based on the value at the time it was acquired. This “base year value” cannot be increased by more than 2% each year, so it is normal for people who have owned their properties for many years to have lower assessments than neighbors who acquired the property more recently. The only other time a property’s assessment would reflect its current market value is if market value were to fall below the Prop 13 value limitation at some point in the future, known as a Prop-8 temporary value reduction.