One part of Expo's approach to UI is to create native user experiences. For several years Expo has invested in React Navigation and Expo Router, which use the system navigator. For instance, in iOS apps made with Expo in 2023, your headers will resize as the user scrolls and layered modals are natively supported. Details like showing the navigation stack when long-pressing the back arrow are supported from day one because Expo apps are native apps that use the system behavior.
In contrast, 2D UI frameworks like Flutter, Silverlight, and Flash replicate the system UI. In my experience it is possible to create a replica that visually looks like a pixel-perfect match but it is very difficult to make the replica behave the same, like the rendering the subtle layer transitions you talked about, invisible boundaries around gestures, and showing the navigation history stack. It is an uphill task and using the native system UI is a tailwind for Expo.
In contrast, 2D UI frameworks like Flutter, Silverlight, and Flash replicate the system UI. In my experience it is possible to create a replica that visually looks like a pixel-perfect match but it is very difficult to make the replica behave the same, like the rendering the subtle layer transitions you talked about, invisible boundaries around gestures, and showing the navigation history stack. It is an uphill task and using the native system UI is a tailwind for Expo.