I don’t fucking know why I can’t eject USB hard drives. I installed the SysInternals apps, and best they can tell me is that Dropbox is fucking with the drives. I explicitly told Dropbox to not fuck with USB drives. I don’t know who’s lying, I just want whoever is fucking with the drives to stop fucking with the drives, OK??? OK.
It generally does not care about files being read/open. If there’s a write operation pending, it just shows that and then ejects.