I think a lot of these are because Apple has built animations into their products as first-class citizens, but that means that they need to somehow figure out how to compose them well. (Which obviously is a rather difficult problem to solve!) In my experience, you end up spending a lot more time trying to get all of the animations to work well together than you do on creating the actual UI, and that time is just not worth it if your start and end states are beautiful and intuitive. There's also the cross-UI-framework tax that has come up since Apple has allowed mixing SwiftUI and (App|UI)Kit, and animations are part of that.