Echoing an earlier Atlantic article, Mary Carpenter suggests we are biased against introverts:

As Barbara Ehrenreich wrote in a Time magazine column about personality tests, "Their chief function as far as I could tell . . . was to weed out the introverts. When asked whether you’d rather be the life of the party or curl up with a book, the correct answer is always, ‘Party!’ " … self-help books that include blatantly stupid questions … paints introverts as "over-critical," "pessimistic" and "anxious," and describes them as feeling "unaccepted, unacceptable or simply inferior."  It’s enough to make an introvert mad. … My enormous, extended and extroverted family still poses a challenge, especially on the small island where we converge for a few weeks every summer. … But the family is making strides in recognizing its introverted minority.

With a little search I find that the shy and introverted both suffer in many ways: 

Introversion is indeed more active than shyness in inhibiting religious disposition.  … Very Conservative males reported the lowest rate of overall shyness. … Non-shy respondents reported the highest rate of starting their own business, … Non-shyness and extroversion reported the highest household income levels …Shyness has a greater impact on the reduction on eye contact than does introversion. … Those with the lowest rates of eye contact achieve the lowest ranks [at the workplace].

We might posit a grand conspiracy of extroverts to keep introverts down, but a more plausible explanation to me is that extroversion is just valued more by society and business.   

I was a shy young nerd and thought I was an introvert, but eventually learned that I was reacting to the fact that other people didn’t like to be around me.  Once I found people who liked to be around me, I loved to be around them too, and was often the last person to leave from a party.   Of course it is possible that my personality changed.