Where capacity allows, serving a route multiple times with small planes is preferred by airlines and customers. And even if slots are restricted, offering less

Where capacity allows, serving a route multiple times with small planes is preferred by airlines and customers. And even if slots are restricted, offering less capacity than demand (driving up prices) can be more profitable than trying to offer service to anyone who's willing to book. Long range versions of single-aisle planes also change the dynamics a bit, putting less focus on hubs.