Because it is actually not easy? Keep in mind Apple has unprecedented resources so not easy is not really a problem for them, as Musk pointed out recently they

Because it is actually not easy? Keep in mind Apple has unprecedented resources so not easy is not really a problem for them, as Musk pointed out recently they've hired thousands of people to work on this. Also I think it has been done to some extent, Tesla's Model S is now (by some measures) the bestselling luxury car, and can probably be credited with accelerating BMW and Porsche moving towards all-electric vehicles.