Let's take a trip back to 1924, when Calvin Coolidge signed the Indian* Citizenship Act.
(*Feather, not dot)The Act conferred citizenship on all Native Americans ("Indians") born within the US to American Indians.
Why would this legislative remedy be required?
Because prior to that, the babies were considered members of their respective sovereign tribes, and not automatically American Citizens, a status previously conferred only on those who had served in the military.
In part,
The act read that “all noncitizen Indians born within the territorial limits of the United States be, and they are hereby, declared to be citizens of the United States: Provided that the granting of such citizenship shall not in any manner impair or otherwise affect the right of any Indian to tribal or other property.”
https://constitutioncenter.org/blog/on-this-day-in-1924-all-indians-made-united-states-citizensAnd here is the undoing of the whole anchor baby scheme. These people, born within the confines (politically) of the United States, on land they or their forebearers had occupied for centuries, if not millennia, were not automatically American Citizens, because they were
subject to the Jurisdiction of their Tribal (national) Government, laws, and customs.
There was even a 'cut out ' provided in the Act if their American Citizen status would negatively impact their rights within their own respective nations.
So, folks, there is just NO WAY someone from a foreign country would automatically be granted US citizenship just for crossing the line from a foreign country to this one before seeing daylight for the first time.