> and a livestreamer likes reuploaders because it helps market their stream

Maybe this is true on one side, but on the other the people who reupload the content will also get revenue from people watching. Since it's the most popular parts, relatively many people will watch it, often completely skipping the stream itself. This means that the original streamer (who creates the value of commentary) has quite a bit to lose from people reuploading their stream.