On Why the Native-Americans of Central and South America Didn't Succumb to European Diseases Like the Indians from North America Did

My suspicion is that it probably had a lot to do with the fact that the colonists and conquerors from Spain and Portugal brought very few women with them in most instances and so when the dudes needed some servicing they ended up impregnating untold numbers of Indian women, the offspring of which inherited immunity from the European fathers. Makes the most sense to me at least.