[quantum_mechani]

Well, if you want the short answer, it's because Mictlan's sacred troops so far outclass all their other options.

The more thematic explanation is that I've increased Mictlan'a racial advantage, with respect to normal troops prices, to cost only 7 gold by default. Perhaps this could be seen as a drastic step, but I have yet to hear anyone complain about Mictlan being more terrifying with slingers than jaguar warriors.