These are not the people writing the articles - that's you and me. The people who work for the WMF are server admins, programmers, HR people, fundraisers, lawyers, lobbyists, finance people, etc.

The staff are there to do things that volunteers can't do, or won't do consistently enough to keep the movement going well. In principle, volunteers could write the code, and at the start that was the case, but volunteers wouldn't have created the Visual Editor, for example.