An itinerary that flies a passenger away from the destination before turning back looks inefficient on a map. It follows directly from how airline networks are built.
The arithmetic of thin routes
A direct flight between two secondary cities needs enough passengers wanting exactly that pair, on that day, to fill an aircraft. For most pairs, that demand does not exist.
Routing both cities through a hub changes the calculation. Each flight carries passengers heading to dozens of final destinations, not one.
The aircraft fills because it is aggregating demand rather than serving a single market, which is what makes small-city service possible at all.
Banks of flights create the connections
Hubs operate in waves. A group of inbound flights lands within a short window, passengers redistribute, and a group of outbound flights departs shortly after.
Each bank multiplies connection opportunities. Twenty arrivals feeding twenty departures produce hundreds of viable city pairs from forty flights.
The cost is that aircraft and gates sit idle between banks, and the airport experiences sharp peaks in staffing demand rather than steady flow.
Why hubs sit where they do
Geography matters less than it appears. A useful hub needs to be roughly on the way for a large share of the traffic it aggregates, but tolerance for detour is wide.
More important are runway capacity, room to expand, weather reliability and the absence of severe night restrictions.
A local origin-and-destination market also helps, because it gives the airline a base of passengers who are not connecting and will pay premium fares.
The trade-off passengers actually make
Connecting itineraries are usually cheaper than direct ones for the same pair, because the airline is filling seats it needed to sell anyway.
The passenger pays in time and in risk. Every additional sector adds a chance of disruption, and the connection is the point where delays compound.
Direct flights command a premium precisely because the buyers who value time most will pay it, which is where hub carriers earn their margin.
Where the model is under pressure
Longer-range narrowbody aircraft have made some thin direct routes viable, because a smaller aircraft needs fewer passengers to fill.
That has allowed point-to-point services on pairs that would once have required a hub, particularly across shorter oceanic distances.
Hubs remain dominant for long-haul, where aircraft size and cost still demand aggregation, and where a single daily departure cannot serve many cities directly.