Comment by immibis

It didn't have enough gold to pay its bonds, so it could either keep the integrity of the dollars intact while defaulting on the bonds, or keep the integrity of the bonds (as measured in dollars) intact while defaulting on the dollars. The latter option allowed it to last a while longer before anyone would notice.

This choice was made some decades before the official day on which the gold standard ended. By 1971, it had already printed dollars to pay its bonds and didn't have nearly enough gold for foreign countries to be able to withdraw all their gold.