>>73769
A couple reasons.
1. Wikepedia editors are predominantly spergouts and NEETS, whose only purpose in life is watch their pet articles like hawks, and undo any "unapproved" edits. This works fine for articles like the history of rubber manufacturing in Guatemala, because the person with the most autism over that subject is also likely the most knowledgeable. For current events/political articles, this means the editor will remove anything that hurts his feelings or goes against his ideology.
2. Wikepedia's editing rules and guidelines are of a complexity that rivals the US tax code. Because of this, chances are you're breaking at least one rule with any kind of edit you make, which means that any passing admin is within his rights to undo your edit if he doesn't like it. So, controversial pages will eventually take the form that the admin wills it.
Unsurprisingly, chronically unemployed spergouts tend to be of a leftist bent. Combine that with the leftist tendency to view oneself as "awsum revolutionary fightan the EVIL BIGOTS" and you have mostly leftist editors under the purview of mostly leftist and highly incestuous admins. If you want an example of this, check out hot-button pages like Breitbart, Trump, etc., as well as their edit history. For bonus points, compare those pages to their equivalents on Infogalactic (a fork of Wikepedia that tries to be more "neutral" with varying degrees of success).