I have one theory: Americans are much more social than French people and expect the French to be as receptive as them to small talk with strangers. But we don’t talk to strangers in France. We value our intimacy bubble and when someone talks to us out of nowhere we feel threatened. There are scripted scenarios for when strangers can interact: saying hi in the elevator is one example (and usually it doesn’t go further). Even the language with its formal pronoun is meant to add distance between you and people you don’t know.

I don't think that's true.

There's a lot of nuance, socialising is a complex mixture of things which varies a lot between and also within country.

People coming with their home expectations and judging others based on it are often just seen as obnoxious and disrespectful from an outside point of view.

As an example, in France it's quite common to tease/gently mock people you're friend with. Some insults can even be used in a friendly way. This is something that doesn't fly AT ALL in a lot of places and, as a french, you have to be really careful with when meeting non-french. If not, you are just being super mean instead of trying to be friendly.

As well, the American way of using a lot of superlatives, being overly excited about things that are not that exciting can been seen as fake and disrespectful, in a lot of other places.

I think it has more to do with the success of the language standardization effort.

AFAIK being very serious about that was a declared goal historically; nation states in general not that old etc, etc..

So you have lots of people that went through a purposefully rigid process in education and of course with that through greater society. At the end there is maybe not much room / tolerance in handling deviations from the norm?

Despite all of that I’ve also seen this changing though as France / the world has become less insular (learning more foreign languages, etc).