The 100% "independent contractor" driver workforce lets them skirt minimum wage laws, vehicle costs, unemployment costs, worker's compensation, Social Security tax, etc. They intentionally flood the market with drivers so customers only have to wait 5 min. Many drivers eventually learn that it's only profitable to drive during high demand times, within urban cores. Logging in during the work day, or in the suburbs simultaneously reduces revenue and increases mileage and time costs. Transportation networks have a fundamental trade off between quality of service and total area serviced.
Cellphones existed before, but not with the ability to install a non-carrier blessed app, with GPS functionality (again keeping wait times down).
The main value add of Uber etc is that they manage the trip so you can have a higher baseline of trust.
Badly. I was scammed multiple times in different countries (I travel a lot), including my own. And there's a lot of uncertainty and stress involved (no guarantee you share a language with your driver, in case they need to ask any questions). And I hate talking over the phone.
As long as that's an option I'm staying with Uber.