I considered myself introvert with problems of shyness, so I have no idea which of my behaviour is due to which. I have no problems running my mouth off in company of close friends, making jokes, shooting the air and so on, but add a stranger to the group and I will shut up.
I value personal space and have a “mind your own business mindset”. Why isn’t an introvert talking? Many reasons. It could be I don’t know you well enough yet and for some reasons I don’t feel like talking about my life to you. I gotten better at making small talk over the time, but!
The second reason why introverts won’t talk is that usually introverts and extroverts have different interests. I am interested in technology and how it works, and why it works and its impact. Extroverts I know tend to talk about technology in terms of how cool it looks, what have they gotten out of it and etc. Of course, I am applying a broad brush here.
For me, I am always constantly evaluating what I am saying, especially to strangers. Are we close enough to talk about this? Is this fellow even going to be interested? Why would I want to let him know this fact? Am I coming across as too biased or open? What does the person really think and wants?
An example - I switched cell groups at church and while talking with people from the new cell group, one asked me “so how are we different from your previous bunch?” and after a while I asked, “Define 'different”. I went on to explain - what differences do you want to hear? The way they relate to another, or their background, or what they do for their activities and etc?
I discover that at least for me, extroverts are okay with being general and non-specific, while I take a longer time to evaluate my responses. Recently, though I have learn to give some verbal cues, such as “Give me a moment to process that” and so on.
The next thing about introverts not talking; well, are you ready to listen to an introvert when he or she talks? To us talking is as good as thinking, so it’s either you wait till we get back to you to and just let you know the conclusion, or you listen to our “thinking aloud” which involves lots and lots of details. And the last thing I want to hear, when I talk, is “You are thinking way too much! Take it easy!” or some such.
Oh I have met extroverts with bad social cues who just keep on talking and talking and cut into other people’s conservations and just sprout nonsense at the drop of the coin, starting new threads of conversations without any context. Not everyone with good people skill = extroverts.