Are they?

The drivers have a certain set of capital and skills, and Uber (and to a lesser extent, Lyft) have created a near-monopoly on the market to buy services produced using that capital and skills. Since the ability to execute a transaction in that market is severely compromised if you don't work by Uber's rules, you are effectively outside of the marketplace if you no longer drive for Uber. You make no money. You go broke. You don't have the capital necessary to effectively compete in the market for giving rides in exchange for money. They own your skills and capital in all but the legal sense.

If there were either real, multi-company competition for Uber's market share, or a larger amount of regulation upon their monopoly, it'd be a different story.

Of course, there are people who think that monopolies are good, but that seems to be counterintuitive to anyone with a basic grasp of human nature and history.