> and there were already better, functional models of how to structure things out there.

Even today, no file sandboxing solution I'm aware of really properly handles more complex file formats that don't consist of a single atomic file.

Only macOS goes beyond the simple "allow the user to pick a single file or directory and that's that" model, and even then according to the documentation I found it only handles simple sidecar files that only differ in the file extension from the main file, but still breaks down for anything more complicated than that.