Selfish people are that way. Both introverts and extroverts. You just might come across more selfish people that are extroverts just by the nature of them being extroverts. Had nothing with them being one way or another.

I would rather spend my time with an extrovert as I have the confidence to be myself while feeding off their energy. Many people feel insecure around someone who is outgoing and will intentionally or unintentionally try to find fault in them.