If we were talking about Uber's current model then you're 100% correct. But if we look at all to where they're going there's tremendous potential.
They bought Otto - which is arguably the leader in self driving trucking and they have self driving trucks on the road right now. If they're able to capture say 20% of the trucking market 10 years from now that's tremendous. They're in a legal fight in SF because they're trying to get self driving cars going. What are their numbers going to look like when they aren't paying drivers anymore?
I'm skeptical of the notion that the big auto manufacturers (who had a conniption fit at the mere notion of Tesla selling cars direct, instead of through a dealership) nimbly setting up autonomous, on demand fleets of vehicles which destroy their dealership network and also cost them half of their revenue.
Yes, they are losing money, but they're playing a very different game than the local taxi company.