No car company on the planet, that I'm aware of, makes air conditioners, as one example. Nor do they make things like brake pads, brake calipers, radiators, headlights, I could go on and on. All these things are outsourced to suppliers. There aren't that many suppliers, and the suppliers pretty much all serve multiple automakers each. So lots of Japanese makers (probably all of them) use parts from Denso, for instance.
It's not that much different from laptop computer makers; there's a bunch of them, all with slightly different designs, but they all use CPUs from AMD or Intel, they all use optical drives from 2 or 3 different companies, they all use memory from a few suppliers, they all use LCD screens from a few suppliers, etc.
Another thing to consider is patents: take a brand-new car apart, and compare it to one from 1996. You'll find a lot of stuff really hasn't changed much (now compare the '96 car to a '76 car, and you'll see a lot of gigantic differences). A lot of stuff in the auto industry has become very mature IMO. Obviously there's a lot of new electronics in new cars (things like lane-keeping assist, radar cruise control, blind-spot monitoring, etc.), but many things look exactly the same: suspensions are about the same, brake systems are identical, the moonroof in my '15 isn't really any different from ones in cars from 10-15 years ago, etc. Patents only last 20 years, so a lot of stuff has probably reached a "good enough" level and the patents have all run out, so companies are probably just doing a lot of things the same way because it's been found to be optimal.
It's not that much different from laptop computer makers; there's a bunch of them, all with slightly different designs, but they all use CPUs from AMD or Intel, they all use optical drives from 2 or 3 different companies, they all use memory from a few suppliers, they all use LCD screens from a few suppliers, etc.
Another thing to consider is patents: take a brand-new car apart, and compare it to one from 1996. You'll find a lot of stuff really hasn't changed much (now compare the '96 car to a '76 car, and you'll see a lot of gigantic differences). A lot of stuff in the auto industry has become very mature IMO. Obviously there's a lot of new electronics in new cars (things like lane-keeping assist, radar cruise control, blind-spot monitoring, etc.), but many things look exactly the same: suspensions are about the same, brake systems are identical, the moonroof in my '15 isn't really any different from ones in cars from 10-15 years ago, etc. Patents only last 20 years, so a lot of stuff has probably reached a "good enough" level and the patents have all run out, so companies are probably just doing a lot of things the same way because it's been found to be optimal.