Easy. The Maya built pyramids. The Egyptians built pyramids. Top JW dogs have always been fascinated with pyramids. They're triangle freaks trying to calculate the "rapture".
You would think with there being 4 earth elements, they'd be into squares. Go figure.
With their love of all things triangular, I wouldn't put it past the GB to think Maya calculations were "special". After all the Maya were excellent mathematicians and astronomers. (Can't imagine who still uses a 365 day calendar 500 yrs after contact ...)
Oh, and from the Yucatan southward, they still speak Itzil and Itza. Of course, if the GB or any one else wanted to know what the calendar meant, they could have simply flown to Guatemala, stood on a street, and asked one of the many millions of Maya walking around ... or called on a cell phone.