Because of how rare it is for someone to Ascend, or even attempt the ritual ( or be given the chance or choice to do so ) there are only ever a few living Baccai at a time. During Azir’s life as emperor, there were five - Iahi being the youngest, and previously an esteemed warrior who served in his own army.
The Baccai are the lowest, classless members of Shuriman society, and live on their own at the very, very edge of the Shuriman city proper. The only one who ever deigns to visit them is Azir, who thinks that by paying homage to them he is earning the god’s favor and further blessing his own Ascension.
The Baccai are all disfigured in their own unique ways, but they all share one common trait - their disfigurements are all likened to snakes. I say this because of what happened to Cassiopeia, and the nature of the curse that was placed on Xerath’s tomb - the Shurimans have a thing for curses and snakes.
I do think you could probably Ascend normally to some sort of snake-like form, but it’s exceedingly rare and not a desirable form compared to others, and are assumed to be less favored by the gods. Snakes in Shuriman culture are considered evil and untrustworthy and sneaky, and are a fitting form for the Baccai.
