They can make phones because they hire/hired experts who can make phones. I doubt they would use those same electrical engineers to design the brake systems. I don't think there's anything evidence to suggest that they couldn't acquire/hire the right talent.
I think you have an incredible misunderstanding of the the due diligence/research that these multi trillion dollar, publicly traded, companies go through to estimate costs/risks of their endeavors.
Looks like that due diligence wasn't diligent enough. But hey, what do I know? I must have an incredible misunderstanding. How could it be anything else?
Personally I don't buy the rumor because I think Apple is smart enough to avoid making their own cars. I think they already learned, by trial and error, that cars are tougher than they look.
When is the last time an electronic mfg had to deal with a billion dollar lawsuit because they didn't follow industry best practices for design like Toyota did after the acceleration scandal? Does Apple have experience with the NHTSB or other relevant regulatory agencies? Sure, there is a lot of gatekeeping in the auto industry, but it's for good reason. Cars can and do regularly kill people. It is not the same as making an iPhone.