No one says they are not needed. It's just that extroverted individuals typically create more relationships within society, and those relationships are usually stronger. However, it's not always the case -- for example, introverted individuals may have a smaller number of relationships, but those relationships may be much stronger.

Society exists because of those relationships, and so it is good for its survival and success if the number of relationships or connections within society is growing and they are becoming stronger. It is basically the existential need for any society.

(I'm sorry if I'm wrong, I'm not a specialist in this field, it's just a bunch of guesses based on my observations)