I'd say the big difference here is running costs. I've worked with automotive clients (Ford, GM, Renault etc) for a while, and that's a big factor for them, especially in the lease market. Also given that a car is not a 'throw it away and hand the customer a reconditioned unit' item, repairs become far more expensive and time critical.

The sheer drag of maintaining a network of repairers, keeping them stocked with (Sometimes huge) spare parts, managing repair times etc is astonishing. I can see why Google and Apple would want to lean on established players instead of going it alone.