I'm wondering if maybe Apple is concerned about US regulators when it comes to self-driving cars and such, especially when in the US it's going to be the feds plus 50 states regulating various aspects, not to mention the highly-litigious environment and a lot of anti-competitive behavior by taxi companies and such.
It's no secret that all these ride-sharing companies are really intending to replace human drivers with robotic cars ASAP, and I'm sure that's the case in China as well. A company like Apple might be able to develop and prove the viability of this sort of technology over in China where the regulatory environment will be more uniform and more relaxed, and not only get a billion customers there working with a popular, established service, but also be able to come back to the US, Europe, etc. with an already proven technology to compete with the likes of Uber who are working on their own technologies and struggling with excessive state and federal regulations restricting their innovative potential.
I sure know I wouldn't want to start a ride-sharing company in the United States, much less a self-driving car company.