Uber is a worldwide company and they have the solid turnover when you talk about the business. There is a competition in all cab companies. Driverless car is the new technology and Uber thought that it will boost their business in compare to their rivals.
If a rival like Google or Waymo developed self driving cars before Uber did, they'd be able to undercut Uber's prices and ultimately drive Uber out of business. That’s the big reason that they have started this service worldwide to compete in the transportation world.