Plane

Airports are banks that fly planes as a side hustle. The actual airport and everything else involved are usually loss leaders. Where they truly earn money is from their points reward system.

They essentially have an unregulated currency that they're the sole source of. They're also the ones that control the supply and demand of everything that can be purchased with this currency.

Banks that offer these reward points need to buy the points from the airline. These costs are then offloaded on any business that wants to accept credit card payments. That's why most businesses prefer cash payments and may even charge a fee for paying with a credit card.