There's nothing wrong with being quiet--besides, most quiet people open up in the right circumstances
I've been asked "why are you so quiet?" before. It's a weird thing to be asked, but I also understand it because people are curious and want to know more about someone who doesn't automatically let others know them by default and doesn't wear their feelings on their sleeve. I'm not always quiet, and friends who know me and have seen me at my most comfortable know that. I used to want to be different, to be more extroverted, but then I realized that it's probably never going to change. So I'm just making the best of it. Most of my friends are more outgoing than me. I think we balance each other out.