Uber needs drivers to have an incentive to maintain their vehicles as efficiently as they can. They want the overall cost of the fleet to be as low as possible,

Uber needs drivers to have an incentive to maintain their vehicles as efficiently as they can. They want the overall cost of the fleet to be as low as possible, because one way or another that cost gets reflected in the price. The current structure preserves that good incentive for drivers, but if they went with a "net" structure they'd have to be much more involved in the purchasing and maintenance choices that their drivers make. That's a really difficult position to be in. (See also the entire health care system.)