Like hotel rooms, airline tickets are a perishable commodity, and unless the airline cancels the flight, there is no major difference in the expenses incurred by the airlines whether there is one passenger flying or 180 passengers are on the flight to a particular destination .
The same amount of fuel will be used by the airline, and fees have to be paid at the airport, salaries to staff, and other expenses. So airlines will always try to maximize the number of passengers in a flight depending on the capacity of the airplane to increase the profit.
During the peak season, there is no shortage of passengers on a particular route, however during the off peak season or off peak hours, airlines will try to maximize the number of passengers, offering low ticket prices to the passenger