If they started to have a 50-80% unit margin, why wouldn't people compete with them? Why wouldn't, say, Amazon compete with them? It doesn't sound like a toug

If they started to have a 50-80% unit margin, why wouldn't people compete with them? Why wouldn't, say, Amazon compete with them? It doesn't sound like a tough business to get into for Amazon -- just buy a bunch of driverless cars. And Amazon excels at competing at close to 0% margins -- why would we imagine that Uber would be successful at competing against Amazon in this scenario?