They did a blog post on it that I can't find right now. Essentially, they made it quite a while ago (2002? I don't recall exactly), and all other options were t

They did a blog post on it that I can't find right now. Essentially, they made it quite a while ago (2002? I don't recall exactly), and all other options were too slow. Their backend apparently has to do a lot of work calculating match scores when users search.