But I wonder: doesn't it need to be accessible to be read locally? If I mine like 1 petabytes of stuff, then I can upload somewhere else and forget about it?
Otherwise they could mine on a disk, then wipe, start again.
IMHO they found a scapegoat, everyone (me included) loves to blame crypto bros for anything bad, but I don't see how here can happen
That's... Not how that works?... You just need to show you have physical hard drive space on your computer. Dropbox doesn't magically give you extra storage...
There was an API floating around ages ago that let you mount a Gmail instance as a virtual hard drive and use it like block device. Dropbox does have an API for file access, so it's entirely possible to write a miner that talks to Dropbox and not your local drive.