You're taking the desktop metaphor too literally. It wasn't primarily about storing everything to the 'Desktop', it was that the UI represented the capabilitie

You're taking the desktop metaphor too literally. It wasn't primarily about storing everything to the 'Desktop', it was that the UI represented the capabilities of the computer in terms of everyday terminology and things people were used to seeing on their desks / in their offices. The 'Desktop' location was just a convenient default location for files but is only a small piece of what the desktop metaphor was about (i.e. you could have a collection of files and folders that you were actively working with on your desktop. The intent was that at some point they would be put away... well, we all see how that went) The desktop metaphor included things like cut and paste to/from a clipboard (back when people actually used to cut and paste pieces of paper this made a lot more sense), files being stored in folders (they were previously more commonly referred to as directories in the text UI world), you put files you wanted to get rid of in the trash etc.