If they said "natural," it would be construed to mean a direct reference to "natural born citizen," making it an attempt to amend the Constitution. Amendments to the Constitution require 3/4ths of the states to ratify.
They tried to be cute about it and substitute the word "native" in place of "natural" with a wink and a nod, intending it to mean one thing while wording it like another.
-PJ