Comment by dwaite

Their focus is investing in areas where they see something being a competitive differentiator, or where the market has failed to create a competitive environment.

They do not make their own screens because they can source screens from multiple sources and work with those manufacturers to create screens with the properties they want. Same thing with them relying on others for electric batteries - there are plenty of manufacturers to provide batteries to Apple's spec.

They created their own wireless modems because there's only one company they were able to purchase modems from, and those modems did not necessarily have the features Apple wanted.

Apple hasn't announced any interest in selling electric cars, solar cell technology, or quantum computing platforms. I wouldn't expect them to do so until they had a consumer product ready for sale. I doubt they are planning to come out with products in any of these categories soon.