Yes, there are two factors involved:
- It’s not just zipping the project from the disk like you are doing in Explorer. That wouldn’t create a safe backup for one thing, since the project is open and some files aren’t kept up to date continually on the disk, to speed up auto-save time. So it’s creating a full duplicate to a temporary location.
- The zip function isn’t Windows’, we can’t tap into that directly. It’s using the library for zipping that we have available, which may not be as optimised, or may be using different settings (high compression rate is slower, for instance).
As advised in the user manual, if you can afford the space usage and are running up against very long backup times, disable the zip option in the Backup settings tab to speed it up. The only thing to be careful of with that setting is to be wary of not opening the backups directly, as they will be ordinary Scrivener projects at that point.