1. As a true blooded introvert, forced socialization is draining. Now multiply that by thrusting me into a contrived scenario, purely for the sake of drawing me out of my "shell," breaking down my "walls" and bonding my inner child to yours; I will find the experience excruciating.
Believe me, this personality trait makes being a believer in Jesus very, super duper hard, because the whole foundation of my faith rests on the nonnegotiable fact that I am called to be a servant to others, that God works through me and that absolutely involves interacting with people. And Lord as my witness, merely attending corporate church services is a mighty act of courage and ginormous leap of faith for me-- to which I'm positive God awards me extra heaps of brownie points for participating (I kid).
2. I don't want to be caught dead in a situation that is embarrassing or makes me feel uncomfortable or awkward. And who does, really? But the nature of these group gatherings are notorious for doing just that. Most introverts don't wear their hearts on their sleeves and small talk rates the same on our fun-list as sanding our teeth on a rock. Unfortunately, these "Team Builders" usually necessitate exercising both criteria to be deemed "successful." And to many of my emotionally extroverted peeps, getting someone to cry is the holy freaking grail.