8.Why can't deleted songs be automatically be deleted from Favorites and Playlists as well?

A: We cannot predict users' preference in this regard and so prefer to keep users' data to err on the side of safety; on the other hand, setting the media library update to check whether each favorited / playlisted song had been deleted from the filesystem has been found to slow the media library update to unacceptable levels, not presenting a plesant user experience.