Fuel burn per seat mile is the name of the game. Boeing won the game with the 787. The A380 was based on long haul high passenger loads. If you can not fill that monster up on the long haul it loses money.
In reality it is a technological wonder. In the future the A380 will fly the sky for many years on long distance heavy loads as a freight carrier which it is most suited for. Boeing will fly the passengers in smaller and more fuel efficient aircraft.
AFAIK no A380’s have been converted to freighters and may not be. Here is one opinion on why not.
“In the future the A380 will fly the sky for many years on long distance heavy loads as a freight carrier which it is most suited for.”
Was it designed with reinforced decks to carry freight, like the 747 heavy freighter? A lifting nose? If not, that would require new airframes. Now Airbus would have to secure customers for that.