Transport adds value by allowing people and goods to move around with less friction. That value is realized by second/third/fourth order effects (bigger labour

Transport adds value by allowing people and goods to move around with less friction. That value is realized by second/third/fourth order effects (bigger labour force available to businesses, money travelling around a wider network causing more price efficiency, improvements in production of goods in one area more effectively being utilized in other areas, all of these things resulting in more tax dollars as well etc etc etc). These benefits are incredibly hard to quantify and likely don't even really directly/immediately affect the people using the transport. If the airport increased prices to try to capture that value in profit they would just be adding that friction back into the system and the benefits would disappear again.