The "files and folders" metaphor never worked even in the heyday of computer literacy, most people never understood it and just dumped all their crap on the desktop.
Seeing as the metaphor did not, does not, and will not work it is only reasonable that personal computing is slowly moving away from it and towards something the users actually want: One singular place to store everything (and I mean everything) and a one-stop quick way to find something in there, organization be damned.
Email is perhaps one of the earliest manifestations of this user desire: Everything goes in the one singular Inbox, and you search for whatever mail you need.