Well, I'm in another game, and can't see your route map, but have you considered flying to other destinations from your destinations. This is something that Southwest (IRL) does out of all its destinations but especially out of Love in real life due to legal restrictions on its flights out of Texas from Love. So instead of flying Phoenix and back, fly to Phoenix and then any countless destinations from there, then back to Love. Then you create a route that goes in reverse with a different plane to pick up the people going the other way along that route. That way you end up with a series of triangular routes all over the country.
Or you can do a strategy of picking a nearby large airport (say, IAH) and flying your planes to there in the early morning (when you have lots of slots available before 5am), then fly out of IAH to long-distance routes, then back to Love late at night. Your plane flies largely empty between Love and IAH (after you put a couple dozen planes flying there there's more planes than people) but you fly profit-laden longer-range flights out of your "hub" to keep that plane moving all day without returning back to your Home until as late as possible (since it flies empty on that DAL-IAH leg you don't want to do that more than once a day if you can help it).