Publishing videos hosted elsewhere might be useful sometimes, but it mostly defeats the purpose of DTube, which is to be an independent video site. Another copy, in case YouTube goes down, or censors your video. This is just hotlinking (embedding), encourages plagiarism and copyright infringement, and brings no discernible upgrade to the users.
What about people who have been deplatformed on YouTube, and need somewhere to upload a video? This feature does nothing for them. It's just a YouTube support function. It's something which was available even on MySpace, 20 years ago.