That could be a part of the contract between driver and uber. You cannot sell to our (uber) clients while offering a service for us.

The driver can set his/her own prices. When they decide which rideshare to use many use price to determine who they want to work for. If they decide Uber they get a scaling scale / surge pricing.

The driver doesn't set the customer price. They can only control the price Uber pays them.. some have asked for more and some have walked over it.