[TrainedMonkey]

My first thought as well, if anything I can think of two reasons why Apple would be building their own car:

1. Compete in luxury electric automotive market. Motivation is there, but I find it dubious that Apple will go for it. On the other had Apple does have everything they need to become strong player in this field (engineers, cash, supply chain, strong U.S. lobbying presence, and army of lawyers)

2. Get competence on how to build cars in order to be able to rapidly prototype integration of Apple products with car entertainment systems. Possibly design said entertainment systems for car manufacturers, or at least influence the design to give apple products an edge.