Maintenance can be offset against manufacturers warranty, why do you think the likes of Ryan Air get shot at about the 5 year mark, the cost goes up post warranty. Only the Military who have no commercial interest will continue flying aircraft that even a third world African Airline would have retired long ago.
Fuel costs and personnel also can be offset as the more it flies, the more revenue it produces and hence again the greater the profit, remember it needs to earn XYZ simply to pay for hull insurance and to service the bank loans on it, you need to clear those to make a profit. Also airborne it's not accruing parking fees
