Why does the rest of the world continue to buy dollars?

The United States continues to finance a chronic external deficit and a growing external debt without any difficulty. Yet, the central banks that in the past provided most of the United States’ external financing no longer do so, since the level of foreign exchange reserves is declining; and the increase in the US external debt is threatening the country’s external solvency. Why does the rest of the world ( t herefore, nowadays mainly private investors) continue to buy financial assets in dollars? Probably because: The Treasuries market is liquid and no one has any doubts about the United States’ fiscal solvency; The lack of a large enough substitute for the dollar; Selling dollars would push down the dollar's exchange rate and inflict losses on the holders of dollars .