There's a lot of things scientists don't know yet.
So who better to ask than the Mayans themselves?
As advanced as these civilizations got, the one thing they DIDN'T know about was micro-organisms and the sources of disease.
Your sources and mine are not of a similar caliber.
Such much of what the world considers "correct" historically certainly is NOT!
Human history is far different than imagined.
As for the Mayan and Aztec Calendars, some things of an astronomical nature work on clockwork time, sure as the Perseids make their appearance in August.
This year August 12th. Tomorrow.
Some cycles are just larger in scale.
It's written into the human chronicle of history if one can just understand it and make sense of it.