Earlier quoted context omitted.
Yachts and planes are physical objects and represent a tiny, tiny fraction of a billionaire's wealth. Wealth is actual ownership interest in valuable companies, which can be moved offshore or the person can renounce citizenship and relocate to a country with friendlier tax laws in the extreme case.
Renouncing citizenship has something like a 20%-of-net-worth tax
A wealth tax would also have the effect that people expecting to generate lots of wealth would just move somewhere else to do so, or not come to the US in the first place.