If a wealth tax isn't going to change anything, then what's the point? Do we really believe that billionaires are keeping their money in scrooge-mc-duck-esque v

If a wealth tax isn't going to change anything, then what's the point? Do we really believe that billionaires are keeping their money in scrooge-mc-duck-esque vaults rather than investing it in diversified portfolios, and that only a wealth tax (rather than the promise of returns on investment) will force them to invest?