Not sure why Ghost doesn’t have a media library. It’s in Ghost’s best interest as far as storage space goes.
If you want to re-use media, you have to keep re-uploading a new version of it each time.
I know you can create a post or page and upload media there and try to re-use it by grabbing the file link, but this is a pretty silly thing to have to do. I don’t recall using any other CMS that doesn’t have a media library.
I remember them talking about the fact that an image doesn’t take much space, so a media library it’s somewhat “unnecessary”. I don’t agree with this statement, and it’s quite annoying having to use 3rd party software to remove the unused images and so on.