People keep bringing it up and it's silly. The huge number is actually a sign of their success. Most of those losses were pegged to equity. In only mildly inaccurate layman terms, it's essentially a promise to give out N shares. When the value of the company increases, say, 10x, the value owed also goes up 10x. For these types of deals, they write it as a loss even though they didn't lose a penny.

They didn't lose any money, though. It's just a promise to give them based on the equity.

If they IPO tomorrow and it turns out their valuation is 10x lower than what it currently is pegged at, the "loss" will magically drop from over $70B to $7B.