Coming from a country whos economy is basically build around cars (Germany) I am baffled by this also. Especially when they think that they can do everything in-house. All the big car companys rely on a ton of suppliers for all kinds of stuff (ranging from drivetrain, to software from ECUs). This means they dont have to worry about a lot of stuff and can basically act as big-time system integrators.
Similarly, I don’t understand why so many people think ICE manufacturers will be able to effortlessly build electric vehicle lines. You can’t just use the same suppliers and infrastructure.
On the flipside, I think it's funny how easy some of the big car companies thought it would be to build a self-driving car. The general attitude I've seen from German car manufacturers the last years was one of "we just need to pour a bunch of software engineers on the problem". Maybe this deal is a start of a mentality-shift there.
A lot of SV companies only know software. And in software it's easy to fix bugs on the product later. Something that's impossible for mechanical things. That's why they all think it's easy to build your own car.
A car is fairly simple, but mass producing it, and getting all the suppliers to work together properly is hard.
Car manufacturers on the other hand have the tendency to treat software like hardware, because the leaders come from hardware. This leads to cultural problems with creating software.
Perhaps publicly, but people tell me that management is acutely aware how hard the problem is; this stems in part from the experience developing the various assistance systems, which was neither cheap nor easy.
Maybe some parts of management, but my impression is that it's also mostly communicated like that internally. I based my comment on conversations I had with people working at the car companies (Audi, BMW, VW and Mercedes), and all expressed that view in slight variations.
Building a car is incredibly easy. Double so if it's electric.
What's hard is (a) building lots of cars as Tesla is finding out and (b) building a perfect self driving car. Now Apple is one of the best companies in the world at manufacturing and as we've seen with FaceID they have a strong grasp of integrating neural networks into commercial products.
So I would never underestimate Apple of all companies.
Building a high-end one-off car is not a huge job. I know people from small teams who've done it. Building a large number of cars at a competitive price is hard, as Tesla found out the hard way.