The lack of visibility is partially because apps can store files in various locations. Outside of the app binaries and such you have their core data, stuff tha

The lack of visibility is partially because apps can store files in various locations. Outside of the app binaries and such you have their core data, stuff that gets generated or downloaded on first run. Besides that you have a cache directory pr app that is housed outside of the tree location of the binaries and main data. More recent Android versions have introduced yet more complications on this via the storage access framework, by providing APIs that give apps limited RW access to "external" storage areas without having to request the related permission. And that's without going into the whole history of just what "external" means when dealing with Android file storage.