Uber drivers get paid an amount based on a subsidy multiplier of the ride value, and they are highly sensitive to these multipliers. According to a driver I talked with recently, Uber takes 20% of the fare, but is currently giving drivers a bonus of about 2.5x. So if a fare is 10 rmb, Uber takes 2 rmb, then pays out 8 * 2.5 = 20rmb. Driving costs these drivers roughly 1-2 rmb/km, and if the subsidy ever fell below 1.3x, the drivers would lose money (these are for People's Uber level of cars, which is the lowest level). Unless the subsidy can ever drop below 1.25x, Uber will be paying for every ride. And if it does, drivers will be parking their cars or switching to another service.
Uber also lost a lot of money through a couple of vulnerabilities that have since been, I believe, patched. Some people were able to figure a way to create fake rides through the app, allowing drivers to get paid without ever driving anyone. They previously also allowed riders to link up Alipay accounts to their Uber accounts, but Uber had no way to ensure the Alipay accounts had funds. So people would take Uber with an empty account, and Uber would have to pay drivers without receiving any money from the riders.
Another side note: there was recently a publicity campaign with some well-known celebrities that had very explicit nationalistic messages encouraging Chinese citizens to use their local service and not the services of an outsider.
Uber will be burning a lot of money in China.