People tend to think that extroverts are like open books and hence easily understood, while introverts are complicated as they don't express their inner selves easily. It's the inability to judge introverts that cause people to be wary of them.
I am also an introvert and the most frequent first impression that people form about me is arrogant, even though I am not. It's probably because humans feel the psychological need to get attention from people around, and they feel inferior when they encounter an aloof person.
Extrovert-ism being critical for success is a false belief that has been fed to us by society. There are plenty of famous people who are/were complete introverts - Einstein, Abraham Lincoln, Bill Gates.
Introverts are not always awkward loners with no friends and social skills, many are just self-sufficient in their emotional needs and do not require constant approval from people around them. Too bad if people are not bright enough to understand that.