New York’s Hyphenated History

"It was only when the pejorative phrasing of “hyphenated Americans” came into vogue in the 1890s, emboldened by Roosevelt’s anti-hyphen speech, that the pressure for the hyphen’s erasure came to pass."

So the claim is that 1890's US anti-immigration campaigns caused such anti-hyphen sentiment that we abandoned the traditional hyphenation of... place names? (except for holdouts such as the New-York historical society).

I am not an academic who studies punctuation over time (surely you exist!) but I... have trouble rejecting the null hypothesis of, like, grammar just evolved, and people increasingly tended to use a non-archaic spelling?

If US anti-immigration campaigns did cause hyphen dropping, why don't we see any big non-American English-speaking place names with hyphens? (New-South-Wales?)

Also, the text itself feels like a stretch; Roosevelt's gave his hyphenated Americans speech in 1915, not amidst the anti-immigrant sentiment of the 1890s