For those who haven’t heard of this, sandboxed apps can request access to a file or folder and persist such access using a security-scoped bookmark. The user however does not know whether the app chooses to persist this bookmark or not; in other words the user does not know whether in each case they are granting a one-time access or persistent access.
There are already folder-specific permissions for every app, including non-sandboxed apps: Desktop, Documents, Downloads. FDA is "everything else". The user has to specifically grant each of those permissions via a system dialog.
With sandboxed apps, you grant access to a file outside the sandbox via a system dialog, open or save. But with non-sandboxed apps, if there were separate permissions for each specific folder, there would have to be separate permission dialogs for each of those folders, and then macOS would become even more of a permissions dialog hell than it already is.
Reminds me of iOS's terrible treatment of PWA local storage. A PWA's offline availability can be revoke at any time the OS decides it knows better than you what your storage should be used for.