Another thing.
It can depend on what you mean by loss making - whether you include fixed costs or not
Say you have 10 airport contracts all alike. Costs £100m a year to run each airport, plus it costs £150m to run the central office, HR etc. the central office functions are fixed overheads - they cost the same whether you run 8 airports or 12
So the total costs of the company are £1,150m. So the break even price for running each airport is £115m. Lets say they all airports are currently contracted at £120m a year, i.e. total revene is £1200m, a profit of £50m
If one comes up for renewal and you bid at £110m that is technically loss making when you consider fixed overheads. But the company overall makes a profit of £40m if you win at that 'loss-making' price, but uf you withdraw from the contract the company profit would only be £30m off £1080m revenue.
Thats the first explanation, others reasons involve price of money (i.e. interest rates), strategic importance, leverage on other contracts etc