Presumably this is intentional -- Uber could raise prices and make more money, but right now they're choosing to keep prices very low in order to undercut Lyft and the cab companies with the assumption that having a monopoly will return more profits in the future. At least anecdotally, here in SF Lyft is almost always more expensive than Uber.
I think almost certainly their profitability is dependent on a future of driverless cars, and I'm sure that's what they are pitching investors. Fearfully, since their survival means going driverless and they are now losing $800 million a quarter, they will race to get driverless cars on the road, it will be rushed, and it could be reckless. I'm thinking the two driverless cars filmed blowing red lights in SF recently…
Once they go driverless, they won't have to pay drivers anymore, but they will no longer have drivers renting them their car at a discounted rate.