What exactly is wrong with one profitable flight, who needs two if the one is a sure money maker? Also, why would a second flight be added if an LCC enters the market when the result is losing money, kinda like the DAL/MCI-STL flights will be.
In Business School parlance, it's called economies of scale. Certain business activities require the same amount of fixed cost infrastructure--facilities, personnel, or equipment for instance--whether you are performing the activity once a day or 50 times a day. It make no sense to do an activity once a day if you have spend the same amount in basic cost that you would have to spend to do it 50 times a day.
For instance, you have an aircraft maintenance facility--say MCI or TUL. You have fixed costs, such as rent/mortgage, lights, gas, 24-hour security. Now, if you repair only 1 plane a day, all of that cost must be absorbed into the "cost" of repairing that airplane. Say, those fixed costs are $1000. Then the true cost of repairing the a/c is the parts and the labor to do the repair (which has to be spent in any case), plus $1000.
If you repair 10 planes/day, then the true cost of each repair is the parts and labor to do the repair, plus only $100 (1000/10).
It's a fixed cost nightmare to run only 1 flight per day to a destination. You still have to have ground personnel, gate/ticket agents, rent to the airport authority, security assessments, etc.
I know there are cases where we do it, but it's something to be avoided where possible.
