So introverts prefer or are naturally inclined to:
take longer to make decisions,
be more conscientious,
have more time to themselves in order to reflect,
avoid small talk
pay attention to experiences
1/5 of the population...apparently careful and thoughtful are necessary, but only in small quantities. We need plenty of underlings to quickly and thoughtlessly carry out our carefully contrived master plan!!
Notice that "less social" didn't really show up. I think that may be beause it's not that they are necessarily less social...but that 4/5 of the population tending to be extroverted means on average you're not going to enjoy socializing as much because the majority behaves in a way contrary to what you naturally prefer. But if it were all introverts, I think the socializiation aspect may end up in the noise.
"Never fear. Him is here" - Captain Chaos (Dom DeLuise), Cannonball Run
Mace Windu: Then our worst fears have been realized. We must move quickly if the Jedi Order is to survive.