Because it exists primarily through promise and agreement ... ie contracts.
Money itself is merely a token of promise/agreement amongst a large group of people that the token money WILL satisfy contracts of all sizes amongst the population.
If a country suddenly decides NOT TO honor the contract of a particular money system ... there's nothing that wealth holders can do about it unless they can bring military force into play to subdue the population of the said country. I think that's called "expropriation" and "nationalization."
So if Joe Rockefeller "owns" pretty well all of the assets in a said country ... and the country says, "sorry, you don't, anymore," this Joe will be SOL and lose his control over what he thought he "owned."
So here's the bottom line, in my opinion ...
To safeguard against the accrual of large amounts of "wealth" ... it's important for countries to be extremely sovereign and have very strong rules against ownership of anything within their boundaries except for citizens of that country. ... and that, in order to own anything within the country, the owner MUST BE a citizen of that country, first and foremost. (No dual citizenships allowed as a basis for trans-national ownership.)
Now, that doesn't exclude LEASING property to foreign investors but ... the leases always have an expiry date and at such a date, the lease could be terminated if the country decides they've had enough. This then ... still allows for foreign investment but prevents control of a country from abroad by foreign owners.
So then ...
If a country suddenly finds itself deeply "in debt" to "someone" ... they can simply declare a debt moratorium -(a temporary suspension of payment or outright erasure of the debt)- set up their own money system ... and operate as a complete independent for awhile until things stabilize again and other countries want to start trading with them again.
What would such money be BASED ON? On the assets and production of their own country.
See, this idea of tying "money" to some distinct commodity like gold ... is really NOT "true" or realistic. I know it's worked ok in the past but it really isn't necessary.
The problem with a "gold standard" or any other "precious" metal or element etc. is that this stuff can be horded too. What would a small country like Iceland do for money if they have no gold in the ground or in the country to speak of ... from the get-go? A country like Africa would then become extremely wealthy ... simply because they can bring gold out of the ground.
If you base money on the assets of a country though ... and on it's potential for production ... and then ON its productive activity ... there's no finite "end" to the amount of money or wealth they can circulate around inside of their own boundaries. You might even say that money for such a country would be a "renewable resource" and that yes ... it sort of DOES "grow on trees" because it grows through the labor of the people.
So the very first step to fix "the systems" is not to go cutting off heads (because those too, will regrow through family propagation) ... but to make sure there are solid laws in place to restrict ownership to citizenship.
You see the big drive by the few "wealthy" people to implement a world government? Why do they want that? Well, once they're totally in control through promise/agreement ... there's no longer any threat to them of losing their "stuff" through nationalizations.
One of the ways to UNWIND the severe damage already done to sovereignty, is to examine all the deals already done and find the FRAUD involved in those deals. If a promise/agreement is fraudulent ... brought on by a deliberate deception or lie and not by good faith agreed to by all parties ... then such a contract can be declared null and void. This might result in the very rich ... LOSING much of what they believe they have.
Similarly, if a country's government has passed fraudulent laws (because the government people are crooks and used deception to operate contrary to the wishes of the people) ... such laws can be declared invalid because they were fraudulently implemented.
Everything hinges on what people will agree to. If a hundred people on an island agree to take the possessions of one fellow because he's so utterly disagreeable ... they win and he loses. The same thing can be true in any country where the citizens agree amongst themselves as to what they want.