Many librarians and library workers are uncomfortable applying the expert labels to themselves. Library school teaches students that there is no such thing as a universally Right and Complete Answer that's more complex than a simple fact-check. Even if those answers existed, many of the people coming into the library don't have enough time to wait for the research and compilation of the information into a useful answer for the person asking the question.
Because there isn't necessarily a right and quick answer, library workers can give degrees of confidence in their answers. This should be enough, but often times, it isn't.