> First you have to line up enough drivers to make it worthwhile, and then get enough app downloads by consumers to make it worthwhile for drivers.

You're assuming that drivers/consumers will be exclusively using your service.

Few drivers are going to drive exclusively for your service. The assumption is that your drivers will already be driving for Uber, Lyft, etc. and will sign up with your service just in order to marginally raise their expected number of rides per hour (hoping that your service might get them a ride when business is slow on Uber, etc.).

Similarly, few consumers are loyal to exclusively one service. They don't care about the difference between Uber and Lyft, they care about getting a cheap ride, quickly. They'll try Uber for a ride. Maybe Uber will be surge-priced. They'll try Lyft, which might not have any drivers on the road. They'll try your service.