Airports spent billions expanding their infrastructure.
You'd have a point if that infrastructure was never
used. But it has been and will continue to be used for a good few years yet.
Oh yeah considering landing and taxiing to the terminal, waiting on the stand, unloading passengers and baggage, cleaning, refuelling, re-loading, taxiing and take-off. It also means reviewing the check-in, security, boarding and baggage processes.
For example, an A380 needs three bridges at the stand for passengers to disembark, instead of the usual two. This has a knock-on effect on the position and movements of ground support equipment like catering trucks and refuelling equipment – more ground support equipment is required for an A380, sometimes up to 30 vehicles and those vehicles can’t simply take up the same positions that they would for a smaller aircraft.
When 615 passengers all arrive at the terminal at once, there’s a risk of longer queues at immigration, passport control, and the baggage carousels. So the airport needs to provide more desks, more staff and a larger baggage collection area.
So yeah all that is huuum well be of dubious value (none) when the masses of passengers expected to land don't show up.