The trip to Mars is pretty long so I think Elon wants his own music service for his astronauts to enjoy SpaceX qualified music. Driving a autonomous car can become boring, so also here only Tesla qualified music. Hyperloop travels: well, that doesn't require music since in a light flash we will be at our destinations. Seriously, when creating the bionic human, integrating the computer with out brains, Neuralink qualified music must be make us even more bionic! :)