Given the fact, as stated in the article that there are a myriad of legal ways by which millionaires and billionaires can skip paying the estate tax, it could very well have been the result of an intentional decision not to evade this by some socially-conscious dying billionaire citizen.
There is also a fair bit left after taxes: "Based on estimates of the average tax rate on estates, the February 2023 payment implied the death of someone possessing a fortune between $17.5 and $40 billion."
