WIPO is about intellectual property. That has nothing to do with human knowledge and everything to do with legal structures to enable government granted monopolies over ideas (patents), expression (copyright), and identification (trademarks).

If anything the "human knowledge" on Wikipedia is the remit of UNESCO, which is "United Nations Educational, Scientific and Cultural Organization".

Wikimedia wanted oberver status at WIPO to be "inside the halls" when WIPO is making decisions that might affect Wikimedia's purpose, which it states as "We help everyone share in the sum of all knowledge."

Because WIPO is a political body and it has nothing to do with truth and knowledge preservation, but about appearance and control.