for people who might still be having an issue with this: an easy way to get the artwork to copy without having to do a whole bunch of additional messing with id3 tags is to organize the music into folders by album with their respective album artwork inside the same folder, then just copy the folders. this worked for me after absolutely no artwork had copied during my previous attempt to just copy the music itself.
apparently android can't read the image in the metadata, so even if a music file has album art embedded, the device still needs an actual separate jpeg or whatever to associate with it so that it can display the art.
this is also the reason that stray jpeg files in the same folder that you keep your music in might be assigned as art to every single stray song in the same folder (in my case making a smug painting of maurice ravel the cover for all of my "unknown artist" songs)