I am surprised that Chinese car companies havent come together to form a common OS platform for EVs. They could had leveraged that platform to make inroad into globally popular operating system for smartphones & tablets too.
It makes sense if you think of it as the car being a giant phone accessory that can move you places, kind of like a personal ride share, rather than an extra phone you don’t need with a car purchase. They’re trying to lock you into an OS that comes with the car and let your infotainment system detach and come with you.
For the consumer facing OS, you can't really leverage a Car entertainment OS into a smartphone tablet OS. The amount of time you spend interfacing with your car vs. your phone isn't even comparable. Not to mention, far more people own phones than cars.
On top of that, the car interface is so fundamentally different from a phone interface. Even between phone and tablet there is no longer a "universal OS", at least in terms of interface.
If you are talking about the bones/underlying architecture, almost everything is using some Unix/Linux/Android variant anyway.
NIO Phone looks like another automaker attempt to find new sources of subscription revenue. BMW was already trying this by making people "subscribe" to heated seats (and recently they announced they would give up on it). Tesla is the closest in which you can pay for some pieces of software like Autopilot later on. People are changing phones quite regularly, so they will try to hitch onto that bandwagon (or at least as a dry run).
IMO, the car has the same limitations as other devices that people have tried to make "smart" (Oven, refrigerator, etc.). The functionality is difficult to adapt to other use cases. When you're driving, you're supposed to be focused on driving (big surprise!), you can't (or at least shouldn't) really spend time ordering pizza or watching movies. If autonomy can improve in the future, then you might have more use cases (ie. literal mobile office) and thus improve subscription opportunities (cloud storage, 5G hotspot, etc.)