If all debters with dollar denominated debt could perfectly coordinate with each other that would be the case. They could all run through your scenario one at a

If all debters with dollar denominated debt could perfectly coordinate with each other that would be the case. They could all run through your scenario one at a time without causing a dollar shortage and a spike in demand and price. But the market is made up of independent actors all of whom want to make sure they get the dollars they need first. It's like a rush for the fire exit with everyone jammed at the door instead of an orderly line.