It makes far more sense for them to focus on software and interface, and leave the bits with engines and wheels to companies which already have ~100 years of research and experience with it.
Lack of manufacturing accumen is Tesla's second largest problem. The main one being what must be a failed culture, given the rate of executive turnover.
While Apple knows how to make things, they make relatively cheap, semi-disposable things where defects aren't lethal.
TMK, they have never made durable goods