You're not stupid! Uber is less vulnerable than DD (mainly because their margins are higher). But it's still a cost-intensive business. Subsidies, local offices, marketing, it adds up. For reference, see [0], although Uber sold their Chinese business to a competitor soon after that article was published.

Also, equity = shares in Uber. Debt = loans. You have less liability when you take somebody's money in exchange for a % of the company, than when you take somebody's money and guarantee you'll pay it back + interest ;)

[0] https://www.bloomberg.com/news/articles/2016-08-25/uber-lose...