world economy has everyone holding huge piles of debt of each other. National banks could agree to zero each others debts out.

Yes, but this not the case for US.

From all US debt, something like $24T is in the hands of foreigners. And not the ones who own something to US.

US exploited USD reserve currency status too heavy, and now owe the world a lot.

After 1970s US trade balance was steady negative, so US import more than export more that 40 years.And if you don't export enough goods to cover your import, the only way to continue is to give obligations. USD is US obligations to the world. That have to be settled.

they don't want to as that is an easy way to print more money

Really it is not a rare thing among countries that owe each other. But that situation itself is rare now, because today countries mostly owe IMF, not another country.