It called Elasticity of Demand. If the the price goes up, the number of passengers goes down.

Raising prices will cause an overall DECREASE in revenue because there will be fewer customers.

Let me say that again: Raising prices will cause an overall DECREASE in revenue because there will be fewer customers.

(The same is true of taxes, but that's another forum...)

If the goal is to maximize revenue, then you price the tickets at the point where the two are maximized. If we could make more by simply raising prices, we would have done so already.