Hm, races are not traits, race features are. Demon is a race, infernal origin is a trait common to all demonic creatures, no matter how their race is called (oni, succubus, devil, demon, half demon, etc).
They also will solve half races problem. If you have a half demon, half angel, you just give this character both traits.
We actually could use the race field to separate for example elves from half elves during events checks. But make them more unique is easier with traits, since you don't want mixed races.