> What you're missing is that the copies aren't being sent to Amazon, Dropbox, or Google.
What you are missing is that the uploading to those services absolutely is a "kind of propagation that enables other parties to make or receive copies." [0] You are, in fact, sending the work to Amazon, Dropbox, or Google, and you are explicitly representing to them that you have, and are exercising, the right to give them permission to make copies of it (and, for some of those services, also to allow third parties to do so.) [1]
> You are no more propagating (another important term defined in GPLv3, which conveying is defined in terms of) a work to those companies than you would be if you put a copy of the work in a storage locker, apartment, rented office space, or even a rented car.
Propagating work is defined as "to do anything with it that, without permission, would make you directly or secondarily liable for infringement under applicable copyright law, except executing it on a computer or modifying a private copy." [0]
Copyright law (at least, in the US) does not make it an infringement to store physical objects containing a copy of the work in space controlled by a third party without permission of the copyright holder. It does, however, make making a copy (including, e.g., by uploading) without such permission, generally, an infringement [2]
So, no, from a legal perspective, the analogy you draw is not valid.
[0] GPLv3, Sec. 0
[1] Consider, e.g., the Dropbox terms of service [3], under "Your Stuff and Permissions": When you use our Services, you provide us with things like your files, content, email messages, contacts and so on ("Your Stuff"). [...] We need your permission to do things like hosting Your Stuff, backing it up, and sharing it when you ask us to. [...] You give us permission to do those things, and this permission extends to trusted third parties we work with.
[2] See 17 USC Sec. 106
[3] https://www.dropbox.com/terms