The point of buying and operating an airliner is to make money. Making money boils down to two points.
1. Most passengers are willing to grit their teeth during their flight in order to pay the least amount possible. To profit in that environment requires operating a twinjet.
2. Airlines also make money moving freight in the belly. To profit in that environment requires a single deck aircraft. Double deckers tend to fill their belly with passenger luggage.
Sadly, as superb as the airplane is, the A380 violates both points 1 and 2.
A lesser but still important point is resale value. Airlines need to be able to sell used aircraft to the secondary market at a reasonable price. That means freighter conversions and high density versions for charter operations. There is no freighter conversion and it is unlikely that a high density version of the A380 can be filled. Right now 10 year old A380s have more value as scrap than as airliners. This may change as later build A380s reach their 10 year point, but this is far from certain.
And even assuming charter operators could fill high density A380s, how many terminals could handle 800+ people disembarking from a single aircraft? And will 800+ people's luggage fit in the belly or would the airline have to restrict the amount of baggage a passenger could take with him/her?
So much like the Concorde which was an engineering marvel, the realities of the market means the A380 (like the Concorde before it) operates in a niche. There's not a lot of profit in niche markets and what profit there is seems to have been mostly captured by a single operator, Emirates. And note that Emirates operate from a huge terminal dedicated exclusively for the A380. Could any airline anywhere duplicate such a terminal? And yes, Emirates operates a whole bunch of A380s, but they ALSO operate even more B777 (indeed they are the largest operator of the B777-300ER) and have ordered hundreds more. So even in the rarified world Emirates operates in, they're buying more B777 than A380. So not even Emirates can make as big a profit flying A380 as they can flying B777, else they'd buy and fly more A380 and less B777.