That's because the dollar is declining as the world reserve currency as a result of the US declining as the hegemon .

The debt will only become relevant after the petrodollar is dead and after countries stop pegging their own currency to the dollar and after SWIFT becomes irrelevant and all the other things that prop up the dollar, and we've already long passed the point where the debt could be reduced enough to save the dollar after it loses its status. The high global demand for dollars meant the debt was irrelevant, but now that demand is on the decline the dollar is fucked and it can not be saved.