Because the original interpretation of “natural born citizen” meant an individual born in the US to two US citizens who had also been born in the US. Cruz was making the point that several current candidates besides himself do not meet that criteria.
He then listed those circumstances. (Cruz was born in Canada to a US citizen and to a non-US citizen; Rubio was born here but neither of his parents were US citizens; Trump was born here but his mother was a naturalized US citizen.)
‘Because the original interpretation of “natural born citizen” meant an individual born in the US to two US citizens who had also been born in the US.’
You are mistaken. The original interpretation of NBC was a person born in the USA to two CITIZEN parents.