Librarians need to be trusted to do research to work in most private and academic libraries. So public libraries just follow the trend. Private librarians tend to focus on organizing databases, since they generally work with computer archives instead of books. Academic libraries do literature reviews, where they read large amounts of research on a subject and then summarize everything they've learned.

Most librarians hop between these fields a few times, and it can be very jarring to adjust to each sytem.