Explained: Big Plane vs Little Plane (The Economics of Long-Haul Flights)
(image credit: Wendover Productions)
Here is a wonderful video from Wendover Productions via YouTube about the economics of long-haul flights. It also helps to show why the airlines may use certain planes on certain routes to certain airports and why non-stop flights may or may not be available and how it may affect the cost of your airline ticket.
It's a lot explained in the 10-minute video and worth every minute to watch.