If you already have a car and are carrying all of the fixed costs of that (a not uncommon case, at least in the US), I think that driving Uber is quite a bit positive financially for the drivers.

If you go out and buy a car solely to drive Uber, I still think you're in the black, as evidenced by the non-trivial amount of Uber drivers who are driving rented cars where the rental company is bearing any long-term costs and bundling them up for the drivers in weekly rentals.

Those drivers are then able to make an easy calculation of "what did I take in this week vs what did I pay out this week?" and I doubt they'd be doing it if that sum was negative or too small week after week, suggesting that when the car rental company's profits are taken out and held by the long-term car-owning drivers, that they should also be profitable.

While it's possible to make a profit from it, time is needed to learn how to maximize your margin enough to reach profitability.