It can be a useful way to extract some value from your car without selling it. Say you are between jobs and have a car you bought new. You would like to keep the car, as you know its history, so you drive Uber to "sell" a part of the car until you get a new job.

You're describing, in essence, a predatory payday loan.

Not really. More like a way to sell a fraction of your vehicle's value while working for less than minimum wage in some cases. Not a great situation but, you are not paying high interest on a loan that you have to pay back.