They did. They just never envisioned that America would be filled with so many simpletons who would be unable to comprehend what they wrote.
So tell me now, Mr. Wit, Are the Russian Ambassador's children "Natural born citizens" of the USA? If you say "no", then you need to stop demonstrating your ignorance. Being born in a stable does not make you a horse, and being born in a manor house does not make you a lord. Your status is inherent in your existence at conception.