Can someone with insight into the matter explain, from a high level, what the big concerns are over Ubers ability to run profitably? In my naive view they are "just running an app" / acting as a mobility marketplace and they make money on each transaction. Given the traction and market dominance they have this sounds like a really attractive business. So how do they manage to run such big losses every year and which…
My guess is that their traction and market dominance are far more fragile than you think. Because their drivers are contractors and not employees, they can't be forced to only work for Uber, so even though they created the pool of drivers, they have not "captured" them. So a huge cost is the ride subsidies which maintain their market position. Once the ride subsidies end, there is no reason that a locally focused company can't compete for the same drivers and riders.
From what I've read, when Uber started their app technology was borderline magical (pushed the boundaries of what smartphones could do), but since that's no longer the case, there is much less of a barrier to entry.