Might sound strange but I don’t think my local grocery store should be allowed to sell their own wares either, because if you operate the marketplace you are inherently biased against competition.
That’s an extreme case sure, but that basic principle applies here too. With software a hardline stance like that is obviously a bit problematic, OS developers should of course be allowed to build nice first party features, but when they sell a general purpose device they have to allow 3rd parties the same access, otherwise they are competing unfairly.
So I have no problem with Apple building hooks in the OS for an AI to access all of the data (should I choose to provide it), but I have a problem with them doing that and then saying I can’t then decide who gets to access it.
I won’t give my data to any of the companies you mentioned, I value my privacy, but I might want to give it to e.g. Proton in the future, if that simplifies my life in any way, why shouldn’t I be allowed to do that?