Another thought regarding The Lost City of Z, and The Lost City of the Monkey God

It is astounding to think that cities the equal (as archealogy is now revealing) of ancient Greece and Rome existed from the Amazon basic in South American, up through Central America and Mexico, and that some mysterious blight struck them and caused the survivors to return to the jungle from which they had emerged centuries if not millennia earlier.  So mysterious.  Was it climate? Volcanic dust clouds? Chicxalub asteroid hit? Disease? Drought?  What could have happened to them over such a large expanse of territory?  The cities were abandoned, not destroyed, as though they were somehow cursed or poisoned.