If they donate the wealth to their own foundation to continue to hold close and control, it doesn't get taxed. If they borrow against the wealth at low interest rates until they die and the basis is stepped up ("buy, borrow, die"), it doesn't get taxed. Certainly, deferment is a component, but there are obvious examples of the very wealthy operating in a manner to avoid taxes entirely when they're able to (realizing the benefit of the wealth without having to realize a taxable event). Trust stacking is a recent fad as well, although I don't have enough data to say whether it is a material concern from a tax revenue perspective.

Silicon Valley Is Obsessed with 'Trust Stacking,' and the IRS Doesn't Like It - https://news.ycombinator.com/item?id=48727963 - June 2026