As usual many here are, factually challenged, to be kind.

We're not "factually challenged." No one is saying that billionaires never realize capital gains on their holdings, or ever sell stock. Bezos has sold - as has Musk, rather famously, to fund his purchases of Twitter. There are other ways to reduce your capital gains exposure besides taking out loans. Especially if one of your interests is philanthropy, since charitable donations have a lot of tax benefits that can be used to lighten the tax load. And if one of your goals in selling stock is to diversify your assets, rather than simply to raise liquid cash to fund ongoing expenses, you can't achieve that goal without triggering a taxable event.

But the build, borrow, die strategy is one that the uber-wealthy can also use to minimize capital gains tax exposure during their lifetimes. Which is why (to return to the original idea) one would expect only modest uptake if, against all odds, the Democrats and Republicans joined forces to provide a limited period of discounted cap gains taxes.