Any two large population centers will have lots of traffic---this does not mean it is the most profitable. A good example is Dallas and Houston. This is where Southwest got their start. This city pair generates many flights but not high profits.

American has announced new non-stop service between San Jose and CDG and TPE. Reasons cited for the TPE run is currently over 60% of their bookings are in business or First on a similar run. They will be using aircraft with a very high ratio of business/First to coach. This looks like a cash cow to them.