Sort:  

Because the community decided they wanted to allow that type of content. Most of us personally hate it.

Well, at least the YouTube videos come with attribution built in, and their own monitization for the author too.. it's actually useful for the original creator of the video to get more views, so I can see why this could be a grey area..

Written works/images done by someone else without any original content added though I would hope to be a completely different story..