There also could be bugs in the hardware that they carefully programmed around.
Raymond Chen has been blogging for close two decades about all of the hacks that MS had to put into Windows because vendors used undocumented APIs.
Where it starts to piss people off though is where those private APIs are used to allow first-party software access to platform features that third-party software doesn’t get. For some applications that’s not so bad, but in the case of a general-purpose operating system platform or similar it’s kind of an anticompetitive move and we should complain when companies do it.
I would much rather an API be private, let the company dog food it and let their internal employees use it, and then make it public. It also gives them the freedom of completely changing the internal workings.
The extensions API and the Siri integration for third parties are great examples. The Siri intent based API is very usable and reminds of the Amazon Lex based API - the AWS version of the consumer Alexa skills SDK.
That's simply not true.
I have no special info, these are just guesses.