I don't work or have ever worked at Apple, so I don't know the full details, but I heard the new design wasn't introduced until very late in the development process, and at a point in time where teams are supposed to focus on polish, not redesigns or introducing new features.

So not only did teams have to rush incroporating this new design, they also didn't get time to think things through and polish. It sounds like they didn't have time to push-back either, and so there was no feedback/iteration loop where they could work out with whomever is in charge of wider system design what works and what doesn't on what apps.