I think you mean "20 years after you die". That seems like a perfectly rational way to deal with people who want to be buried in their gold and jewels in a pyramid.
OK, so you can have your dad's piano for 20 years after he dies, after that it's public property.
Some people would surprisingly agree with that.
Well, yes; some people would agree with the stronger proposition of you not getting that piano, or not without paying some tax on it.
How on earth do you classify estate taxes as stronger than fixed term ownership?
I don't, but, I mean, when someone comes and takes some of your money, then it means you had a fixed term on owning that amount, which just came to an end.
"Stuff taken away" is "stuff taken away", no matter what angle we take.