This has a lot to do with Wikipedia being designed by a couple of Objectivists. They believe there is one reality that can only be correctly perceived in one way, by Rational Individuals. Wikipedia is the encyclopedia for that worldview, and it excels where there is little disagreement between worldviews.

A better Wikipedia would have epistemological relativity as a central mechanic, while simultaneously relaxing the rules on acceptable sources. Implementing that in a way that doesn't compromise UX would be difficult, but it's a technical problem more than anything.