...and government jails private individuals that attempt the same thing. They're called Ponzi schemes, and are all about paying off previous investors with intake from new investors.
They are portrayed as a savings plan for retirement, but are legally a welfare system -- a transfer of money from current taxpayers to the favored group.
Previous generations never payed enough, and current generations will never get out of it what they contribute. That inflection point was passed ten years ago, IIRC.
And the SS savings is a joke, as the government just loans it to itself and spends it. This means when it's time to start pulling out this "savings" to use it on retirees, government will have to tax or borrow it anyway to pay itself back.