PC's of a couple of decades ago provide a parallel. Microsoft getting 10's of dollars of margin off every PC, Intel getting 10's or maybe 100+ dollars of margin off every PC, and motherboard makers with a gross margin of $3 per board. Much less the case makers....
The old line auto manufactures are building cases for the computers and software that are tomorrow's self-driving cars.
It's a large consumer market that's changing rapidly and ripe for disruption. Why would you doubt that Apple will enter it?
The real reason I think Apple would pull the plug on it's car project, is if they believe we are about to move to a transportation as a service world. Ride sharing and self driving cars are trends that point in that direction. Apple is a (consumer) product company. Their internal structure is set up to make the best consumer products and sell them directly to consumers. They are not set up to be a services company. Being a (successful) services company is to some extent antithetical to being a successful product company. Apple knows this.
Perhaps not "insurmountable"...
...but you realize that what Apple currently manufactures is equivalent to one single, near-insignificant component of what goes into a car: the on-board navigation system.
Building a car is hard. I don't think Apple can't do it, but I'm convinced they won't find it "worth it".
[1] https://en.wikipedia.org/wiki/Transportation_as_a_Service