Human speech has evolved to make use of the frequencies that we can hear most effectively. Audiologists only test the range of speech frequencies because this is what we concentrate on restoring. While it may be interesting to note someone can hear ultra low bass sounds, or 10kHz and above, it has no clinical significance so we don’t take the time to test it.
The majority of hearing loss starts very high and works it’s way down. So children tend to be able to hear high frequencies over 8kHz, but by the time they’re in their twenties they have a “hearing loss” if you like, because they can no longer detect them. Because it’s outside of speech frequencies though, it has no effect on their lives and isn’t tested or treated.
Likewise people may or may not have a very low frequency loss, but we’d never know because they don’t test for it.
So all hearing loss is effectively in speech frequencies, because otherwise we don’t consider it a loss.