Wikileaks has also leaked things the Russian political establishment almost certainly doesn't like, e.g. https://wikileaks.org//spyfiles/russia/.

Apparently Wikileaks were given documents that had already leaked elsewhere before and refused to publish them because their purpose is novel leaks, not repeating leaks from elsewhere. That has been spun into a narrative that they refused leaks because they are biased, without much evidence.

When there are a lot of disingenuous arguments like this being made to discredit someone that turn out to be unreasonable once you dig a little deeper, like we see with Wikileaks and Assange, it generally is a strong suggestion someone is trying to manipulate people into believing a false narrative.