This was AFTER the 14th amendment passed.
If citizenship was granted just by being born in the territorial limits of the US there would have been no need for this act.
Yet it was.
The logical conclusion is that being born on US soil is not enough.
Elk v. Wilkins, holding that simply being born on U.S. soil is not enough to confer citizenship. Also see the Congressional debates on the 14th am., making it clear it did not confer birth right citizenship.