You say a bunch of stuff about how it's the same old same old, and ma and pa can set up a file sharing server and figure out syncing between all the computers t

You say a bunch of stuff about how it's the same old same old, and ma and pa can set up a file sharing server and figure out syncing between all the computers they use. The comments on TFA and yours all miss the point. You touch on it in parentheses at the end. It's easy. Normal people don't have an always on server they can administer and have reliably available. It is literally sign up, install tiny program, put files in a folder. Done. This isn't a problem people didn't have, it was a very real and common problem, hence the success.