It’s more of a throwback to an age where the majority of the apps are creators and editors of documents embodied as files on disk, giving users the freedom to move, rename, copy, and otherwise organize files. As soon as apps began to manage their own data storage through a SQLite database or even the cloud, the File menu stopped making sense. We still keep it because we are romantically attached to it and it harkens back to an age where users had more control over data storage on their computers.