That is because Natural Born Citizenship (as defined by Vattel, and understood by the founders) is not the result of any statutes, or legislation, or legal action of any kind.
A Natural Born Citizen is one born in the country to two citizen parents; there is no question of citizenship, or of any natural allegiance to any other country, and therefore no need for any legal action or legislation to define their status.
Of all the presidents of the USA, all except two have been born in the USA to two parents who were citizens at the time of the president's birth. The two exceptions were Chester A. Arthur and Obama.