Last attempt. California can levy a tax on billionaires when they spend money, leverage assets or anything else they want, but said billionaires can just leave the state (and have been doing), they are inherently incredibly mobile. A single state cant do anything about that, especially when there are conservative states that will bend over backwards to accommodate the billionaires. Taxing land means the asset cant be moved under any circumstance and so it is a far more attractive option to tax.