You're kinda selling the Maya short there. The Classical Greeks weren't unified and they are in as a Civ. The Maya left numerous remains of socially/technologically advanced cities. The other Mesoamerican cultures (Zapotecs, Olmecs, Tarascans, Mixtecs, Totonacs, Teotihuacan) aren't as well attested in history and potential leaders as the Maya, thanks to the successful decipherment of the Maya glyphs. I would consider the Maya more important than the Aztecs in the grand scheme of things, especially with regards to Mesoamerican history. Yet unfortunately, stereotypes and pop culture has enabled the Aztecs to be present in the game since Civ1.