Finns are known for being quiet? (And Swedes for being noisy?) Not a lot of either people here in my part of California so I wouldn't know. >.>
I think being the slightly introverted, calm type is quite much part of the Swedish and Finnish self-images. There might be some truth to it, but I guess some of it is just cultural stereotyping.
"Why are you so [insert personality trait which is seen as negative]?" are the most hideous and stupid questions a person can make. Anyone with a bit of social intelligence should totally avoid them.
People are the way they are just because they are like that, they haven't decided to be like that and there's no valid reason they could give you. In any case, those questions are often more an aggression than a genuine search for explanations.