It really doesn't make sense for Apple to manufacture traditional cars - they're expensive to produce, have steep support requirements, allow limited driver interaction points to avoid distraction, etc. Apple's strength is in combining hardware and software in a way that makes interaction intuitive. If you have to actually drive your car, there's not a whole lot of room for that beyond what's already being done with CarPlay. It makes a lot more sense to create an autonomous vehicle and treat the entire cabin as an interactive experience that people will spend hours a day playing with and spending money in.