If the operation doesn't make an economic profit, and if there isn't sufficient moat to defend the operation until it can become profitable, then I agree with you it's not worth anything.
But in fact, Uber does have a massive moat -- its network of drivers and riders in thousands of cities around the world. No competitor is even close.
It takes tremendous capital expenditure to build that network, and it will take tremendous capital expenditure to neutralize it.
It remains to be seen if Uber can make an economic profit, but with an operating loss of just 10% of gross revenue, it's not at all inconceivable.