If you mean a scientific legacy, it is not clear to me that this is true - Thomas Jefferson was Virginian, and though he was a 'lesser' scientist than Franklin just over the Mason/Dixon line, he was quite significant.

But supposing it is so, there are so many reasons it seems to me difficult to find out which were most critical.

• The Greeks were largely surrounded by less erudite regions (at least, immediately so surrounded). Not so with the southern states, which were competing with the north and Europe at least.

• When the Greeks were taken over by the Romans, the Romans spread their Greek Wisdom(tm) far and wide. The North... didn't.

• The Greeks had far more time to produce work of note.

• The southern states had resource extraction economies.