Both of those wikis were started specifically to promote an ideology (conservatism, and internet atheist subculture, respectively.) Nowhere in the charter of Conservapedia is any admonition to be unbiased! "Be conservative" is in their name! (And their slogan, and their site rules...)

The same is true of Rationalwiki, but less directly. It was created by the promoters of a specific ideology, and as the chessboard of subculture politics evolved, the fact that the people who posted there were generally inclined toward promoting ideologies proved to be a more stable trend than any particular ideology. Right now it's one kind of leftist, but in the future it could evolve into a breed of leftism, or something else entirely. In any case, it will probably go on being ideological in nature, as it always has been, right from conception.

Wikipedia has done relatively well as far as political bias goes. Emphasis on the word "relatively," but it's not the worst thing ever. Jimmy Wales is the best person to lead an attempt to repeat that state of not-abject-failure, because we already know that he is a reliable supporter of democratic principles and sticking to the facts. (Democratic principles including the democratic principle of averaging the opinion of everyone who shows up.)