When the WMF was set up, those involved chose not to make it a membership organisation.

Greetings!  I will emerge from the shadows to point out that WMF was originally incorporated as a membership organization, with criteria for membership, public pages about membership and discussions about how to implement the details.  However, its articles of incorporation were later changed under very likely illegal circumstances (through a vote made without informing their membership).  It's very possible that the many original members still have the standing to remedy this unfortunate situation of a self-appointing Board—if they can organize such a push.

The long story: https://meta.wikimedia.org/wiki/Wikimedia_Foundation_membership_controversy

Regards,
[[mw:User:Adamw]]