Troubleshooting & messages · Moves and copies that didn't finish
Why won't Storage Studio move my Mac's temporary area to the external drive?
Short answer: The temporary area is scratch space every app needs at all times, so it can't live on a removable drive. Storage Studio offers to clear what's safe there instead.
Your Mac's temporary area is scratch space every app uses, often before the external drive is even connected. If it lived on a removable drive, apps would fail whenever the drive was away. So Storage Studio offers to clear what's safe to clear there instead of moving it.
See temporary files.