[Fraxinus]

IMO, it is due to the less dramatic combination of more stability in south and central America along with new tools that the researchers have had ten years or more to get results from. It takes time from the ID'ing of a prospective site to the excavation, and even more time from the start of excavation to publishing in scientific (often very narrowly focused)journals, then even more time to publication for the general public.

[wyattearp]

Not to mention the remoteness of the archaeological sites. These sites aren't in the open; they are buried in jungle. A city looks like just another patch of rain forest. Once something is found, the next massive problem is getting there. This stuff is being found literally in the middle of nowhere.