Apparently because a lot of folks in the Roman Empire had snake pets. A lot.
Snakes and ferrets were more commonly used as “mousers” than cats were, except in Egypt. And cats (or ferrets) didn’t usually live in the middle of the desert.
Also, a lot of highborn Romans or rich Romans were very into snakes as companions, to the point of wearing them around the house or letting them slither around the tables at banquets. (Non-poisonous snakes, mind you.)
So desert monks having desert snakes as pets, mousers, and bodyguards was actually kinda mainstream, for Romans. I didn’t realize that.
Aliens in This World 