Introverts often perform brilliantly when pitching or persuading. Being out in front of others is not their relaxing place, so they focus, pour their energy into it and succeed at it.
I think with all the real and pop science done the past few years on introversion and it's subsequent rise in awareness, far too many people conflate social anxiety and introversion. They may be related but they're not the same thing.
Then they withdraw to some solitude to recharge.