This seems like a riskily reductionist point, as we know that people aren't always single-issue voters focused on achieving their financial best interests.
However, the anecdotal evidence of "stored wealth vs current income" tax is there, notice how "let's-back-tax-everybodys-income" Prop-30-happy California is also home to "dont-you-dare-to-raise-taxes-on-my-mansions" Prop 13. My original remark was to point out that wealthy people and high income people are frequently advocating opposite causes.
Mansions? Hardly. More like "Don't raise taxes on my tiny tract home through the roof based on ridiculously inflated real estate values."
Maybe in a state that didn't have both high sales taxes and high income taxes a cap on property taxes wouldn't make sense. But in California it does.