Although there are few publicly owned airports left, those councils that need to sell are legally obliged to sell it at what is described as 'best value' for the local ratepayers - and quite right too as they are the 'real owners'.
Whilst value could be defined in a number of qualitative ways, most take the safe view that it means price. Saying that a council 'screws the airport' is a bit irrational.
The private sector is not in the business of municipal pride - it is there to make a profit. Period. Sadly these days that tends to involve ripping off people to park and providing over priced shops rather than putting dots on the route map.
When the private company sells on, it will do so at the best price it can get - it is obliged to its shareholders to do so.