There are a lot of countries they have never published anything on. They have a smaller number of large leaks, so that is not necessarily out of the ordinary.

I think it is credible that Wikileaks were provided some documents from Russian state-sanctioned actors, who knew Wikileaks would publish them, and that the state-sanctioned actors did so to serve Russian interests. But the claim that Wikileaks as a whole is biased towards Russia doesn't seem likely.