> Why aren't Apple's apps themselves also having to ask for permission?

If you look at the list of example reasons [1] that would require an app to ask for tracking permission, they are (broadly) in two buckets: correlating and/or consuming user data from multiple sources, and sharing data with a data broker for advertising purposes.

Apple does not share data outside of itself, and their apps do not display ads.

-- [1] https://developer.apple.com/app-store/user-privacy-and-data-...