It hasn’t happened yet because it hasn’t happened yet.
Simple as that.
The analogy I like to use is someone living off of credit cards and using cash advances from one to pay the balances of the other. If someone can get enough credit cards, they can keep this game going for years. If they could get an infinite supply, forever. But in a world of finite credit supply, it will all ultimately come crashing down.
For America, the credit cards are creditor nations. And there are enough of them to have kept us solvent up till now.
Something that kept the game going for as long as it has is that Wall Street managed to convince the world that the bond ratings were actually meaningful. Once enough AAA stuff turns to junk over the next year or so you can bet they will stop financing our debt.
