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.

This is obviously a fallacy under our current economic system; workers are not "free to choose whatever job/occupation" they'd like. Their circumstances (material conditions) dictate what they can and cannot do for work, and in some places, driving for Uber is about it, at least for a part time gig that can fit around a primary job (since many Americans at least must work in excess of 50 hours a week to afford food and rent).

So, instead of punching down and saying "man, just get a better job" we could recognize the realities of the world and hope we can make the conditions of drivers better. Uber, or a system like it, at least if we are forced to have car-centric infrastructure, should be a net good. At the moment it is not.