I don't know why you think this: the French are explicit (and proud) of both their cultural chauvinism and their willingness to integrate those who fully assimilate into it. Assimilation is required, but it's also sufficient (in contrast with the US, where it's neither required nor sufficient).

> The idea that you move to a country and you're one of them is an American concept.

Not a very old one[1].

[1]: https://en.wikipedia.org/wiki/Hyphenated_American