> I am describing things as I see them
But you're not.
> Once people there have established their friend groups they’re not looking to add any more to the group
Is an observation
> as they worry too many new friends will diminish their own place in their friend group.
Is an interpretation.
Perhaps you've met someone that told you this is what's happening to them. But that's an individual, not a blanket assumption you can place across all the locals.
Source: I am a PNW local. I wasn't born here, but have been here since I was a kid. Here's the thing about your point about "insincere nice". It's not insincere. It's just delusional.
I met lots of people. I get excited about lots of them. I mean when I say I want to hang out again, or show them around. I can visualize a future where we do those things. I want to leave the door open to that happening.
But I get busy, I get tired. I make tough choices. And this new person ends up getting prioritized at the bottom of the list.
I know the criticism. This is mean. It's cruel. But it feels meaner to say "i'm too busy to hang out" to someone who i genuinely like and feel like if things lined up well, we could become friends.
If I say "let's hang out again soon" and we never do, I wasn't lying to you. I was lying to myself.