I don't see what scales, their costs are per person/vehicle there is no way with their model to see a reduction in costs by acquiring new drivers. Even if you remove the driver and can have fully autonomous cars the costs are perhaps marginally reduced in the long term. The way they burn money I don't think they have that long of a term in them.

I always believe their intention was to become big enough and ubiquitous enough that they could become a monopoly supplier and therefore set profitable prices without the risk of being undercut, having consumed or removed their competition through subsidised rides.