A file copy of the contents is not a preservation of the original media in its entirety. There might not even be any "files" to copy, depending on the platform

A file copy of the contents is not a preservation of the original media in its entirety. There might not even be any "files" to copy, depending on the platform (many Amiga games would bypass having a filesystem entirely and access data in a raw, direct manner). Working with disk images allows recovering "deleted" contents, or otherwise recovering data from "slack space" (say, if a file was edited and shortened, the data after the new end of the file in the final sector is likely still present).