I guess they do that to not get a "connection" with the person in question. On the opposite, a technique to win someone over fast is to be nice and open about yourself from the beginning although you don't know him at all. If you like someone you might let slip something through (without even realizing it). I base this opinion on my experience with grading students. Some people can get really good at it. I do it aswell so I know what to look for and try to avoid being "too nice".