Originally Posted by HarryT
Because its main purpose is to act as a Mobipocket Reader for desktop PCs. The ability to manage external devices is a very minor aspect of its functionality.
For a Mobipocket format book, that is indeed the case, yes. Mobi Desktop Reader lets you "edit" this metadata, but it's not actually changing the metadata in the original file; it just stores your changes in a separate file with a ".mbp" extension.
tompe's excellent "mobi2mobi" tool allows you to genuinely edit the metadata in a Mobipocket book.
YOu could copy the mbp file along with the main file to get the metadata.