The problem is that theres a lot of stuff in the tax code that allows those at the higher end to also defer taxes indefinitely. So not taxing estates/inheritance, and allowing these deferrals leaves assets untaxed at the high end forever.

For example, step up basis allows inherited assets to have their cost basis re-struck at the value at time of inheritance. So if there is no inheritance tax, the assets transfer to a new owner and a large chunk of value is forever untaxed, even when/if they eventually sell.

Similarly all sorts of interesting stuff that can be done with trusts. Again stuff that's only accessible / worth the hassle to 1%.

In a world with extreme outcomes due to scaling, we might accidentally be re-inventing the hereditary aristocracy if the assets can accumulate outside the tax system.