"Taxing billionaires" is the left's version of "cut Medicaid fraud." It's a message for low-information voters who have a gut feeling that free stuff will require more taxes, but get confused converting from billions to trillions: https://www.washingtonpost.com/opinions/2020/03/06/msnbc-sug...
That's why Democrats say "we're the only developed western country without universal healthcare," but never "we're the only developed western country without a 15%+ VAT."