Maybe this is a big-city perspective, but I've understood that the main constraint driving aircraft size is runway capacity during peak hours. Airports already require a lot of land for handling a relatively small number of passengers. As building additional runways is often not feasible, the only way to increase passenger capacity is using bigger aircraft.
I fly between Helsinki and London often enough. On that route, the aircraft is typically either an A320 or an A350.
I fly between Helsinki and London often enough. On that route, the aircraft is typically either an A320 or an A350.