User blog comment:Susanolivia/Fixed Width, Sidebar, and the Removal of Monaco/@comment-1488341-20101001034237/@comment-3100721-20101001040916

Apparently it was to get readers to contribute with the removal of easy access to "system" pages that would confuse the reader (Looks at MediaWiki:Sidebar and Monaco-sidebar, now why did they put Special pages next to Random page to begin with? It's amazing that people stayed with that setup.), make the layout easier to understand for the newbie et al.