User blog comment:Susanolivia/Fixed Width, Sidebar, and the Removal of Monaco/@comment-75.71.39.16-20101001171603/@comment-761251-20101001183739

Monobook doesn't have many features that Monaco has. It runs fairly fast because of that, but doesn't give you the full user experience that Monaco gave you. Keeping Monaco running on heavily used servers taxes them more than Monobook does, and more than "Oasis" will. That's why it was redesigned. However, when redesigning Monaco's internals and cutting down on expensive features, Wikia could still have stuck with the old look, or updated it not so much -- for example, they could have kept the old sidebar, but moved it to the right.