So many times I've been in a normal taxi and wanted to rate the driver. Knowing that if they were held accountable for the truly horrible service they would never drive again. This is part of why Uber is awesome.
Restaurants and traditional taxis did it first with tipping.
Tipping has been proven, through data, to not affect quality of service received. Better to simply pay staff a real wage.
Except that tipping has actual value, and does not lead to termination.