I chose not to automatically delete words because it would be unexpected behavior for the export feature. Instead, users have the option to delete all words manually if they no longer need them. So after you export, it’s easy to delete words—just select all of them with Ctrl + A and press the Delete Selected button.
This is the best option I see after careful consideration, but I’m open to more suggestions.
Edit: The Delete Selected button is not yet available in Lookupper and will be introduced in the next version. However, you can still delete words in a similar way: click on the list, press Ctrl + A to select all, and then press Delete or Backspace to remove them.