Part of this is that Uber was / is building a rider / driver base, and to do so, they accept losses on every ride. They were paying drivers more money than they were collecting in fares. It was an attempt to claim market share and drive competitors out of business (which hasn't quite worked thus far) so they could increase the prices later when they had price control power. Uber's existence is all based around investors dumping money faster than they burn it in operating costs (without ever turning a profit).

Driver quality correlates with price/earnings per mile on an S-Curve. Per mile earnings and per mile prices have both dropped.