Many airlines only offer flights to their hubs and "focus cities", there's not enough demand considering other airlines that already service that route. I live in Pittsburgh and Jet Blue only flies non-stop to Boston and JFK, Southwest and AirTran have non-stops to Orlando. There's not enough demand for every airline to service that route non-stop, they would rather funnel you through their hubs. USAir recently dropped their Pittsburgh-Orlando non-stop, they could not be profitable on that route with the competition from Southwest and AirTran.