> Once people there have established their friend groups they’re not looking to add any more to the group as they worry too many new friends will diminish their own place in their friend group.

That's such a cynical interpretation of a totally reasonable problem of social dynamics.

A friendship of 2 has different dynamics than 3 than 4, etc. And all of them are different depending on the composition of intraverts/extraverts.

FWIW, the extravert friend groups I know are highly inclusive and are always eager to add new members. For obvious reasons.

And the opposite for introverts who are much more careful and cautious (I am one) because they know how fragile good vibes can be and how new strangers are exhausting and can affect them.

IMO, the Pacific Northwest attracts introverts because the main activities are fairly individualistic (hiking, skiing) and the social aspects happen before/after which you can easily skip. Not so in something like NYC where everything is orientated around other people.

Then extraverts move to the PNW for the hot tech job markets (Seattle/Vancouver) and are annoyed that everyone is so "cold".