Why should they [framers of the U.S.Constitution, Madison et al.] need to clariy something they all knew?
The Constitution is not a dictionary.
The definition of natural born Citizen appears in the holding of SCOTUS’s unanimous decision of Minor v. Happersett (1874).
Minor v. Happersett, 88 U.S. 162 (1875), is a United States Supreme Court case in which the Court held that the Constitution did not grant women the right to vote.
The Minor v. Happersett ruling was based on an interpretation of the Privileges or Immunities Clause of the Fourteenth Amendment. The Supreme Court readily accepted that Minor was a citizen of the United States, but held that the constitutionally protected privileges of citizenship did not include the right to vote.
SCOTUS rejected Minor’s argument that she was a citizen under the 14th Amendment of the U.S.Constitution, and examined her eligibility, concluding that she belonged to the class of citizens who, being born in the U.S. of citizen parents, was a natural born Citizen, and not covered by the 14th Amendment. This holding has been used in 25 consequent SCOTUS decisions since 1875.