It's not an invisible hand. The riders rate the drivers. The drivers have to maintain a 4.6/5.0 rating. The most common reason for negative ratings is lack of local knowledge. There are other things that get them instantly deactivated, like sexual harassment.
I've recently started driving for Uber part-time.
I've wondered about the professional nature of taxis, though. Ubers and taxis have both had good knowledge of the roads in my experience. Both treat me well. Taxis often seem to smell bad, and Ubers have not. Ubers seem to arrive at my location to pick me up faster. I've had limited experience riding in either, though.