It's not just or always about security. Authorship presupposes that the person working on a particular project has the ability and right to claim the ideas and work in it as their own. In fact, no idea happens in a vacuum, and many projects often have multiple people working on them (editing, designing, etc.). Sometimes claiming that a work comes from nobody can be a way of acknowledge that it's actually coming from everybody.
Also, it can be a way of avoiding celebrity, whether positive or negative.