Why would a race constantly deafened by ambient noises still hear?
In a story that I'm writing, there is a giant waterfall which flows down a cliff face. The waterfall is extraordinarily large, and the torrents of water which flow over the side are deafening.
Behind this waterfall, within the rocky face, is a cave system in which a race of humanoid fae lives. While the caves allow protection from the elements and many predators, the echoing caverns provide no relief from the noise of the water.
Instead of relying on audio, they instead have evolved a strong sense of smell. Like some real-world species, the fae can detect direction and distance of their prey and predators based on stereo input into their sensitive nostrils. Additionally, they have developed a complex language involving a combination of pheromones and visual sign.
With all this said: I can justify their continuing to have ears to aid with balance and intracranial air pressure. But why would such a species have retained their ability to hear with these ears, in an environment where they are unable to hear anything besides the waterfall anyway?