Is there an available API/service that does the trip tracking part of Uber? Of any technical challenge that would present a bunch of clones popping up, I can see that being one of them. The rest is just generating an invoice and accepting a credit card payment. Obviously, not to scale, but for small-medium-sized locales, it could suffice.
There already are lots of Uber clones. You can buy Uber-clone code to start your own.
The hard part of cloning Uber as a company is building both sides of the market. It's almost impossible to do without a clever strategy and tons of cash.
That's simply not true. Places where Uber and Lyft aren't allowed have a thriving alternative ride-sharing economy. In Austin, there are 3 different Uber-clone apps that do a fine job: Ride Austin, Fasten, and Fare.