Bigger planes are the airlines' answer to crowded hubs and rising costs.

Faced with crowded airports, rising prices, a lack of pilots, and a rise in the number of people who want to travel, airlines are turning more and more to the same solution: bigger planes that can fit more people.

According to aviation data company Cirium, the 11 biggest U.S. airlines had an average of more than 153 seats on domestic flights in 2018. This was up from an average of nearly 141 seats in 2017. Even though there are 10.6%....