A docx document of Microsoft Word is actual a zip archive. You can open it and see why some documents are so large yet contain only a few pages.
By simply removing the media item I left the document corrupted. Word tried it’s best to fix it and showed me what was recovered. Then I found out the image was used in a bullet defined in the template. But I don’t use bullets.
Word renamed the other images in the media folder to start the numbering from 1. My document of 3 pages has shrunken from 2 Mb to only 140 Kb. I achieved this by removing what wasn’t needed.