Difference between Greek prefixes "dys-" and "caco-"

Maybe my Googling skills are failing me, but from what I can tell, both prefixes mean, "bad, poor, ill, evil." So why is one used instead of the other? Why do we have cacophony, and not dysphony. Why dysphoria, and not cacophoria?

https://redd.it/1wuyr0k
@r_etymology