This still doesn't make any sense. If you are losing money working for Uber, then you do have access to a higher paying alternative - which is literally standing in your house and doing nothing. Because zero is greater than a negative amount.
I think there are really three explanations that make sense:
People are not literally losing money working for Uber, or maybe they are sometimes but not overall at the end of the month, and they're just rhetorically exaggerating in frustration.
People are literally losing money working for Uber but only when you include depreciation of their car, and that is a long term cost, so people are effectively taking a loan from their future selves.
People are literally losing money working for Uber but morally feel that they should be working rather than not working, even if there is no economic reason for them to do so, and they just hope their situation will improve in the future.
I believe this is it. They need money now, Uber is better than a payday loan but yes, they are mortgaging assets to make some cash now.
People are literally losing money working for Uber but enjoy driving as a hobby, and Uber helps them recoup at least some of the costs of driving around all the time.
(yes, I've had drivers tell me they do Uber/Lyft for fun because they love driving)
Nobody wakes up in the morning and says "today I'm going to drive for Uber literally for free." Of course not. Let's use a little common sense here.
Uber drivers expect, plan, hope to make money. The point is, they don't make much, and sometimes it's very little (like on a long fare).
So the question is, then why do they keep doing it? And I'm just suggesting that maybe a lot of them don't have a higher-paying alternative that they are dumbly choosing against.