I know jpegs are a lossy format. They degrade if you change/re-save them. Does that happen if you repeatedly save a draft in which you have already embedded jpegs before you publish — but without actually resizing the images or doing anything else to them? Does just repeated re-saving of the draft do anything to the images?
The draft you are saving continues to refer to the image you uploaded to wordpress. You are not re-saving the image. The image is saved in the “media library” and saving in the text editor only saves your new text and references to your already uploaded image in the “media library”.