While some currencies from developing nations fail, it just doesn't happen with those from rich countries, because the country has the assets to intervene if there's trouble. With stablecoins, when things get bad it just dies and goes to nothing.

There are incidents where a national currency winds up getting devalued, like when Soros bet against the UK pound. But proportionately that's a small decrease in value, the pound didn't go to zero like failing stablecoins do.