If they spent $1 Billion improving their service it's better than trying to outspend a natively innovating company in China backed by local people running under different rules.
Uber has to be in China because they raised $RIDICULOUS on a valuation of $MORERIDICULOUS. That valuation is premised on the idea that they will somehow be part of the fundamental physical infrastructure of the world, in a more-than-just-taxicab kind of way. Disclosure: I think that this is an absurd premise. But it's their ambition.
So they have to eventually show solid steps on being more than just a taxi company for rich dense North American cities, because they claimed they were worth $MORERIDICULOUS. They have to pursue some more ambitious schemes. One of those is getting a dominant position in the market of the 1/7th of the world that is most rapidly growing in wealth.
And it's for the same reason why you want visa everywhere. Even if everyone uses unionpay, the travellers want their visa cards to work.