Achievements are often used to guide players through a site's many features, doesen't matter if it's directly gameplay related or not, (and in fact, they are, this is a multiplayer game where you constantly interact with other people even if unknowingly), if this achievement were removed, we'd have an unexplored site feature that is generally accessible to every user, and would that make sense? Not really.
It's just an achievement, and while I know there can be a weird mishmash between people's general social anxiety (which can be overcome, even if crippling) and completionism (we did just well without achievements before and can be ignored) it is a very minute one.