A fare that looks dramatically cheaper than the alternatives frequently finishes at a similar total. The difference is in what the base fare was ever meant to include.
The base fare is deliberately minimal
Low-cost carriers strip the ticket down to a seat and the operation of the flight. Baggage, seat assignment, changes and refreshments are separate purchases.
This is not concealment so much as a different product design, and it works well for travellers who genuinely want only the seat.
The gap opens for travellers who need a checked bag, a specific seat or the ability to change plans, since each of those restores a cost the fare removed.
Secondary airports move cost onto the ground
Cheaper landing fees at outlying airports are part of how the fare is kept low, and the saving is real for the airline.
For the passenger, the same choice adds a transfer that can take an hour or more and cost a meaningful fraction of the ticket.
Where the transfer only runs at certain hours, an early or late flight can also force an extra night's accommodation onto the trip.
Schedule design shifts risk to the passenger
Low-cost networks are usually point to point, with each flight sold as a separate contract rather than as a connection.
A missed onward flight after a delay is therefore the passenger's problem rather than the airline's, and the replacement ticket is bought at short notice.
Full-service carriers selling a single connected itinerary absorb that risk, and part of the fare difference is the price of that absorption.
Tight turnarounds have consequences
Aircraft utilisation is central to the economics, so schedules are built with short ground times and few spare aircraft.
That works cleanly on a normal day and recovers slowly on a bad one, because there is little slack in the day to absorb a disruption.
The same efficiency that produces the low fare is what makes late-day delays propagate further than they would on a network with reserve capacity.
The comparison that actually settles it
The honest comparison prices the identical journey on both options, including bags, seats, ground transport and any accommodation the timing forces.
Done that way the low-cost option still wins often, particularly for short trips with hand luggage and flexible arrival times.
It loses most reliably on long trips, family travel with luggage and any itinerary where a missed connection would be expensive to repair.