The vast majority of Jacob’s descendants elected not to return to Israel in the days of Ezra and Nehemiah, preferring the lives they had made for themselves in other nations during the Assyrian and Babylonian captivities. 587 years later (or thereabouts), when James wrote his epistle, the twelve tribes were still largely “scattered abroad”, and this almost two decades before the Romans sacked Jerusalem in AD70 and dispersed the Jews yet again.
It may be argued that Jacob’s descendants have been “in the midst of many peoples” and “among the nations” for the better part of the last two thousand years. Israel is still scattered abroad today, despite the existence of a national home for the Jews. Seven million live in Israel, while 8.25 million live elsewhere, six million in the US alone. And these are just the ones who identify as having this very specific type of Hebrew background.
In a sense, then, there is nothing new about what we are about to read in Micah.