I know this is a dead thread, and OP has no interest, the topic is still worth mentioning.
Nobody is completely introverted or extroverted. It's more like how much you like sweet food and salty food. Like most things that we see as binary (i.e. gender) it's more of a spectrum. People also forget that we have shy extroverts (someone mentioned something similar earlier).
Reasons why extroversion is viewed more favourably: they're 2/3 of the population, as most things go the thing which is majority is always seen as good. They're more likely to put themselves out there, talk to everyone, so everyone has some sort of general idea of who they are.
Being introverted isn't always a negative, yes small talk will make them seem super awkward - but if they see it as being meaningful they will openly talk.
There was a test done, where there was an extroverted leader put against an introverted leader. They were told that they had to fold 200 t-shirts. Both teams got given a team member who would suggest & teach the 'Japanese' way of folding clothes if asked.
The extroverted leader quickly told everyone what to do, and didn't hear out the Japanese way. Where as the introvert took the time to take in everyone's suggestions and decided to do it the Japanese way. The introvert team finished first.
This is not to say either is any better than the other.
Bias information: As an introvert, I think I connect the best with other introverts and feel I have more meaningful relationships with them.