If GM manages to build self-driving cars before Uber, why wouldn't they just acquire a third tier Uber competitor (someone small enough that they don't have to

If GM manages to build self-driving cars before Uber, why wouldn't they just acquire a third tier Uber competitor (someone small enough that they don't have to pay for tons of existing users, but big enough to have made a reasonably functional app), kick out the human drivers replacing them entirely with self-driving cars, then undercut Uber's prices driving Uber out of business? It would be much, much easier to get close enough to Uber's app functionality to compete with them than to get close enough to a self-driving car to be able to use them for millions of riders.