Your question on the IMF is a good one. Many people on this page have hinted around this question, but none have asked it.
The IMF does not accept "haircuts" on its debts ("haircuts" translates into reductions in Net Present Value of obligations). The IMF is a political organization that is funded by its members, which consist of the world's wealthier countries. The IMF's lending decisions are often more political than economic. For example, Venezuela recently asked the IMF for financial assistance, but was turned down. On an economic basis, Venezuela checks all the boxes for an IMF lending facility. Politically, especially from the perspective of the majority of nations that fund the IMF, Venezuela is an untouchable rogue.
When countries borrow from the IMF, it is known that there won't be a restructuring that reduces NPV. When private creditors buy sovereign bonds, all the protective covenants are designed with potential restructuring/default in mind. When private creditors/investors buy sovereign bonds in a country like Argentina, their calculations include the lending position of the IMF. As Guzman and creditors negotiate today, the sanctity of the IMF debt to Argentina is a given. Blackrock et al's calculation of what Argentina can afford to pay is based on the IMF coming out whole, at 100 cents on the dollar.
Debtor nations and private creditors go along with the IMF as an untouchable lender for several reasons. The most persuasive reason is that the IMF is the world's lender of last resort. When a country desperately needs lots of cash with few strings attached, there is only one source: the IMF. The IMF was active during the "Tequila Crisis," which originated in Mexico years ago - before my time. It was also uber-active when Southeast Asian economies were near collapse in 1997. Since then, the IMF has come to the rescue of numerous countries on an ad hoc basis - think Greece in 2010 and beyond.
No country wants the political fallout of stiffing the IMF. And no country wants to be on the grudge list of the international lender of last resort. You never know when a black swan event will occur - like a chinavirus pandemic, for example.