Recent article stated Apple was beefing up their lobbying arm. The car might be the main reason. Even if this car comes to fruition, Apple is still going to have to spend a ton of money on ancillary lobbying efforts to get the cars sold in various states. Currently dealership owners in several states have a monopoly on selling cars. Tesla can tell Apple all about the shenanigans of state and local politicians when it comes to selling cars without franchised dealerships. It's a clusterf.
On topic: I think Apple is only going to be able to use a contract manufacturer to build this car. No branded manufacturer is going to cede control like Apple wants.