In my opinion it is not just the age of the aircraft and the cost of maintenance and the route structure, but the general attitude and "culture" of management and the employees.

Look at Southwest - even now, when they have added lots of connecting flight itineraries and long hauls to their usual short hop point-to-point service, they are still making money. I know some don't like the "cattle car" boarding or the inability to upgrade, but everything else is handled so well and people treated so well that they are now attracting some of the most hardened road warriors.

This is a service industry, and the companies that provide the best service and make people feel welcome will succeed. Those that don't, won't.

Just my opinion.