User blog comment:BertH/Fluid layout is arriving on December 4/@comment-5079375-20131127024048/@comment-957747-20131130011126

That's because these types of elements are against the Terms of Use as they cover up other elements of the Wikia skin (and Monobook) on different screen resolutions and make it impossible for users to interact with those elements of the skin. Elements within the article space cannot be moved outside of that area.