Protect themselves from what? Uber is under no obligation to charge you any amount based off of route, zone, etc. They can charge you whatever they see fit and pay their drivers whatever they see fit. If you don't like the charge, don't take the Uber! If the driver doesn't like the fare, don't accept it!
In case you haven't noticed this is how ALL middle men make money. They charge more to the end user than they pay for a product.
Even your contracting example makes sense. You pay for a deliverable. Does it matter that it costs them less to get it to you and pocket the difference? Nope. That principle is the backbone of all commerce. You charge more than it costs you to deliver.
in this case the middleman is telling a different story between the user and driver. uber is, allegedly, charging the user a higher price while showing the driver a lower price so that they are pocketing extra money that should be going to the driver. say uber takes 10% off each transaction by contract. if they charge the user $10 but show the driver the ride is $8, then by paying the driver $7.20 instead of the deserved and agreed upon via contract $9.00, then they are skimming "hidden" money. this is highly deceptive.
this is how a middleman in a more seedy emplyment scenario gets their fingers chopped off because they're making extra money on the side from the business transactions.
In case you haven't noticed this is how ALL middle men make money. They charge more to the end user than they pay for a product.
Even your contracting example makes sense. You pay for a deliverable. Does it matter that it costs them less to get it to you and pocket the difference? Nope. That principle is the backbone of all commerce. You charge more than it costs you to deliver.