The fact that the original upload text description/post body is not alterable via Steemit means that it's stored elsewhere and is not the same parameter as the Steemit post/comment. I'm guessing it's because comments are disabled. If the text is stored in the metadata that means that someone can very well upload thousands of one second videos with maximum text and overwhelm Dtube. (I'm assuming that the meta data/text is not being stored solely on the Steem blockchain but is instead mirrored/forwarded onto the Steem blockchain from its initial destination -- correct me if I'm wrong).