In short, the airlines realized the Boeing 777-9 has a better future. Lower seat costs and no need for very expensive dual-level jet bridges at airport parking gates does help things. Watch Emirates buy an additional 50 777-9 planes in place of the 30 A380’s they were going to order.
Not only specialized terminals, but if memory serves, needed longer and stronger runways as well... putting most of the existing infrastructure for passenger travel unserviceable by this behemoth.