Why are JPG files not rotated when viewed?

Only some file types (like RAWs) are auto-rotated by default. These are images which can't be rotated and saved to file.

JPG files may be set to rotate automatically. To do this add the extension(.jpg) to the "auto-rotate these file types" at the bottom of the Application Settings dialog. Neither DBGallery nor programs such as FastStone actually auto-rotate the file to disk. It's simply viewed upright. Both programs do of course rotate to file when manual rotation is chosen. So the only difference between DBG and FS is that DBG doesn't have jpgs set to auto-rotate.