Why when I search for a ticket between two cities do I have to chose a specific fare zone?

Why when I search for a ticket between two cities do I have to chose a specific fare zone?

On some of our routes, the cost of travel differs across our stops. While in the same city, the stops may require different fees based on distance from the destination. We ask you to choose your specific stop or 'fare zone' for your origin point, so we are sure we are charging you an accurate fare price, and you can board the bus with ease once you arrive.