That’s not the net worth of the US Federal government, that’s the net worth of the entire USA—including Bill Gates and Jeff Bezos, all 300 million citizens of the USA, and all of their businesses. 75% of that net worth, according to the Wikipedia article, is American households and non-profits. The federal government “only” has about $5 trillion in assets and $16 trillion in debts (these numbers are from 2014 and are thus out of date—that debt is now up to $26 trillion, while I don’t believe the assets have increased significantly). The state governments actually have more assets and less debt, holding almost $14 trillion in assets and about $5 trillion in debts.
While the federal government’s assets are still much larger than theirs, Bill Gates and Jeff Bezos together have $300 billion in net worth, 6% of the federal government’s assets, and that’s taking into account their debts. In addition, that’s including federal assets that are very difficult to liquidate (they can’t exactly start selling aircraft carrier) while Jeff Bezos could sell his Amazon stock and still wind up with a huge amount of cash, even if it isn’t all of his current net assets. Given that the federal government has a wide range of projects, including the US military, and billionaires could focus on a single issue like homelessness or climate change, they could potentially do a great deal in accomplishing their goals.
You’re correct, I misread the page. I wasn’t able to easily find any reasonable comparison of “net worth” of the US or state governments—measures tend to mix up “hard” assets like current land value and gold/currency reserves with “soft” liabilities like pension or legislative promised payments. Nothing I found looked at the discounted present value of future taxation—billionaires are mostly heavily invested in a few companies, and their wealth is a fractional ownership of a “value” that is a large multiple of those companies’ annual earnings. Government accounting just isn’t done the same way.