That would be because, at least on my star, this is simply instinct for them. They do not pull the aether from their own bodies, but from everything else around them.

[ Which means they instinctually know how to command such magicks. Though also why most creatures have some kind of elemental alignment or another. Not all, but some. ]

Which, really, is something that Spoken races have to learn to do. Yes, you can use your own personal aether, but that is what drains one's lifeforce. White magicks rely on an understanding of the elements themselves while black magicks tend to rely more on aetheric stamina. Typically speaking, one has to maintain the balance of their aetheric stamina by alternating between umbral and astral states.