User blog comment:Sannse/Important Updates on Wikia’s New Look/@comment-1504498-20100928235021/@comment-122657-20100928235317

They can't monetarily support multiple skins. Having Monobook for Unencyclopedia and it's sister projects and Anwers for the Answers wikis will already be straining their abilities. They have to reduce the amount of code they're responsible for, by making everyone else use the same thing.