My contributions to Stack Overflow have all been done anonymously, and I haven't ever felt even the slightest bit of desire to link that identity to my real one, add it to my resume, brag to friends.
Having and sharing knowledge to me is its own reward, and I have no intention of profiting from it in any way.
Your own personal way of thinking about the world shines through when you search for ulterior motivations and state as fact that those factors, like a desire for fame or money, must be present.