The government wants the taxes on that money, now. They want it because they know that it is more than the a person is likely to spend in their lifetime, and they don’t want to wait until the wealthy die.
They would like to take over all the money, and pay it back as an annuity, but they know that anyone who accumulated anywhere near 3 million dollars in a retirement account isn’t about to allow the government to manage their money.
Sort of like what the Hilde-beeste (Hillary) wanted when she wanted to take over people’s 401(k) plans. Give it back with just 3% interest and the government would keep the money.
And to top it off the unused money in those plans can be passed on to heirs. They can’t have that!