They have? Details, sure, like structure of debt and who the creditors are (things like the IMF didn't exist previously), but countries still default.

https://www.rstreet.org/2016/02/22/countries-dont-go-bankrup...

https://en.wikipedia.org/wiki/List_of_sovereign_debt_crises

https://www.bankofcanada.ca/wp-content/uploads/2016/06/r101-...

In any case, defaulting on debt is completely natural. It is what's part of how the system is supposed to work. If lenders didn't pay attention, out of lack of knowledge or willfully, and the debtor cannot repay, that's it. There has been a very successful campaign that strengthened the side of the lenders, big and small, over many decades - not necessarily consciously and deliberately (not a concerted effort). It's been successfully made into a moral issue.