Pardon my simpleton, what is the insurance element for ?
Let's assume for sake of argument that you're a billionaire. According to the financial math, you should have no problem assuring that you'll enjoy at least a basic lifestyle for the rest of your life. And that's true, as far as it goes. So is longevity insurance worthless to you?
No, not worthless. It has some value. How much value we could quibble about perhaps, but zero is not correct. And the reason is that billionaires also live in/among civil society, and really the only force that's keeping them billionaires is a government (or governments) that enforce private property rights and contracts....
....With a caveat or two. What governments giveth, governments can also take away. A government can seize assets under color of law. All assets, in fact, except for assets that are explicitly protected from forfeiture under the law.
Theft, fraud, and gross incompetence are also possible. Government tries to defend private property from theft, but even the best run police force isn't perfect and doesn't always recover assets. There's a recent example here in Singapore. A Singaporean allegedly violated United Nations and U.S. sanctions against North Korea, and the United States government has thrown the book at him. While he might not have lost
all his wealth, for sure he's been whacked hard and continues to be whacked. He's now on a "Denied Parties" list, nobody reputable (or even semi-reputable) can touch him, and he probably has lots of assets frozen. It's hard to know for sure how the U.S. government has impacted his life, but it's not fun. And the U.S. government can do all that, legally, even if he's innocent. Many governments can, actually.
Anyway, a relatively small amount of high quality sovereign longevity insurance is very, very cheap insurance against "SHTF" catastrophes. The asset protection aspects have value. Most wealthy people understand this value, which is why I continue to wonder whether the people who don't understand this are as wealthy as they claim.