The society uses a lot of ways to separate class.
The most obvious way is the real estate price, the real estate price decided who are your neighbors, who are not. After they use the real estate price to control who would be your neighbors, they use the fare to decide how you can go. Obviously, they don't want someone living in a slum area often appears in a high-end residential area, so they use the fare to block them. They don't want to see the real world they made as no one want garbage going out from the junkyard and appears in front of their home.
I remember that when I was a child, some kids are far more informed for different places in the world because their parents bought them many of international tickets, I was very very jealous of them for what they can see in such age, all of these is unfair.
Fare evasion, just some little tricks to gain back that little bit relatively fair.