It's not the 2011 iOS anymore, if an app today hides its video projects from the user, it's entirely the app fault.
I imagine, for example, that if the internal project files for a popular video editing app were accessible, we’d see competing and/or open source apps emerge that could parse them, were the original app to become suddenly unavailable. Instead they’re just lost because your phone won’t let you access them.
while possible, it is fairly non-trivial for iOS apps to have read/write access to a shared folder where they can drop arbitrary files, which can then be accessed by other apps, or be discovered by the user. it often requires copious permission negotiation handling codepaths by the developer, and a fearlessness of scary permission-warning dialogs by the end-user.
even on modern (commercially popular flavors of) Android which no longer imbibes the "free software" ethos of the linux core the OS was built around, you can't access formerly accessible application sandbox folders without installing third party browsing tools or plugging into a desktop computer to mount the storage, and cross-application sandbox access is similar to iOS.
in the "personal computing way" mentioned by the article (even today on desktop environments, less so on MacOS) program outputs are default-visible, and developers have to go out of their way to firewall or obscure or encrypt it from being accessible by the user or other programs using OS-provided pathways.
i think this is 100% on the OS + hardware + application platform provider (with Apple as all three on iOS).