That is not how capitalism works. Uber drivers are responsible for both fixed and variable costs. The marginal revenue of a fare might be less than the marginal cost and the decision to accept a fare needs to be made by the driver. If Uber drivers do not have the ability to make revenue management decisions they cease to be contractors. Uber is misleading its drivers and the IRS by labeling its drivers as contractors and passing losses onto them.
Uber Black in Washington D.C. is basically exclusively run by private limo operators driving Escalades. Owners of recent model $70,000+ cars are not your typical Uber driver, and do have other sources of income.
Almost every Uber black driver I've taken has handed me their card and proceeded to upsell me on their services outside of Uber.
I don't have any personal experience driving, would be nice to have a clarification on that.