The money has to come from somewhere
Airports cost a lot to build and run - whoever owns them has to get a return on the captal otherwise you're running a subsidised oepration and someone (eg the rate payer or taxpayer) is paying.
If you sell the asset to the private sector - becasue you can't afford to pour money in for updates etc - they're going to want to turn 10% at least profit over investment to be competitive in the stock exchange. Public Sector might want 5% margin butthey are constricted on what they can borrow for investment
If income continues to slide cp passeneger growth you'll get more over crowding, more "inovative" charges, less maintenance etc etc