I think because the metaphor went from being file-centric (you choose the file, you launch the app) to app-centric (you open the app, then open the file). It's

I think because the metaphor went from being file-centric (you choose the file, you launch the app) to app-centric (you open the app, then open the file). It's not exactly applicable to the file manager arena but I guess most users do not need to manage files, they let their apps do it for them.