The additional cost to the airline to pre-book seats is de minimis. Their ticketing and websites already support it. The purpose of charging to pre-book seats i

The additional cost to the airline to pre-book seats is de minimis. Their ticketing and websites already support it. The purpose of charging to pre-book seats is to obscure the all-inclusive price of the ticket and to increase overall revenue. As a result of this is that it is more difficult for consumers to compare ticket prices between airlines, and consumers are more likely to pay more than planned for airline tickets due to surprise charges.