This sounds a lot like the Greek culture, and I always find it a bit uncomfortable to engage in smalltalk when I travel to a country that does it. It's a very specific type of smalltalk, like what you'd do at a bus stop or at a house party, where you're just talking to the other person superficially without any intent to continue any sort of relationship after you've gotten to know them a bit.
I can't explain it very well, but smalltalk is talking to just pass the time until something else happens. We tend to think of talking to someone as a bit more meaningful, and meant to create or deepen a relationship, so if we know that we're never going to see someone again, we tend to just not make an effort to talk to them.
Your point about the "super-nice new friend" rings especially true, as that's what I find most uncomfortable. It just seems extremely fake, and that's not to say there aren't friendly people in the US, it's just that specific interaction where they're being fake-super-friendly as part of a transaction or business relationship.
I can't explain it very well, but smalltalk is talking to just pass the time until something else happens. We tend to think of talking to someone as a bit more meaningful, and meant to create or deepen a relationship, so if we know that we're never going to see someone again, we tend to just not make an effort to talk to them.
Your point about the "super-nice new friend" rings especially true, as that's what I find most uncomfortable. It just seems extremely fake, and that's not to say there aren't friendly people in the US, it's just that specific interaction where they're being fake-super-friendly as part of a transaction or business relationship.