Not to mention personal risk if you consider how dangerous some Uber drivers are.
However if you consider the cost of car maintenance, annual depreciation on a taxi-like vehicle, and petrol the fares are actually very low. I would be willing to bet that a lot of Uber drivers are wavering around breaking even on the long run. Maybe that's why a lot of drivers' cars aren't as well-groomed as they used to be.
Now, I get that "from a consumer perspective" this is irrelevant, but it does mean that a cheaper service is simply not possible without sacrificing something.