Do cheap tickets actually impact airport revenue? My understanding is that airlines pay a set price per takeoff and landing. So airports should generate constant revenue regardless of fluctuation in ticket prices.
Part of the airport's willingness to give Ryanair a discount is the expectation of full planes with a lot of seats, so there are more people to sell to.
e.g. [1] Table 6, Warsaw Modlin airport charges Ryanair 6 PLN (€1.30) per passenger, vs the normal 40 PLN (€8.50). That's obviously significant when they sell flights for €15 or so.
[1] https://www.researchgate.net/publication/317710545_Internati...