Why Don’t Any US Airlines Fly The Airbus A380?

While the United States is home to the world’s three or four largest airlines (depending on the metric), it doesn’t operate the largest passenger aircraft. No US-based airline ordered the Airbus A380 Superjumbo, even though Pan Am had been the first to fly the Boeing 747-100 Jumbo in 1970. United Airlines operates the second-largest fleet of widebody aircraft after Emirates, and yet it didn’t order the Airbus A380. But why?