Easy. The A380 has extremely limited utility. There are only a handful of airlines for which it made sense (EK, CX, SQ), and only about a dozen superhub airports in the world where it made sense. 20 years ago Airbus placed a big, disastrous bet that superhub-to-superhub traffic would explode by now, and require many hundreds of VLAs, operated by dozens of airlines, to overcome slot capacity limits.

Simultaneously Boeing placed an entirely different bet with the 787, namely that the real growth would be in Tier I-to-Tier II city pairs over long distances, e.g. AUS-LHR or EWR-GLA.

Boeing was right and Airbus was wrong. The A380 is not suited for Tier II markets; it's too big. (Even Emirates came to see this in the last few years and backed out of its last tranche of A380 orders, killing the program.) Some airlines that were considered natural operators like CX said no, and most others took only a token smattering (BA, AF, QF). Even the megacarriers are voting for long-leg nonstop services between superhubs and Tier II markets, eg. LHR-PER, which the A380 cannot perform, and even it could, would never fly full.

The US airlines learned from the 747 experience the dreadful cost of imposing an oversized aircraft on secondary markets. Only UA kept their 747s around through the 21st century. AA parked the last of theirs in the 1980s, and DL, EA, National, etc. got rid of their 747s quickly in the '70s. 747 costs helped kill Pan Am. With those cautionary lessons in mind, no US operator was ever a candidate for the A380.

Some A380s have already been retired and there is no used / secondary market for them.

Airbus only sold 30% of the aircraft it needed to in order for the A380 program to turn a profit. Its insistence on taking the plane to market on the basis of such faulty / illusory market forecasts will be the basis of horrifying business school case studies for years to come.