It’s a bit of a mistake to think of a sensorineural hearing loss as being a “loss of volume” that can simply be compensated by a “gain of volume”.
In the cochlea are an array of tiny hairs which conduct sound patterns to nerve receptors, which then send signals to your brain. The brain receives the signal patterns and interprets them as sounds. It’s somewhat analogous to the old crawler signs at your local bank that would display the time and temperature as a pattern of dots – your eyes would see the dots, and your brain would then interpret those patterns as letters or numbers.
In a sensorineural hearing loss, some of the hairs and/or nerve receptors that pick up the sound patterns are non-functional. Thus your brain no longer has as clear a pattern from which to interpret sounds, especially verbal communication. It’s like having some of the light bulbs in the crawler signs burned out, so that you have difficulty distinguishing between a “8” and a “3” or the letter “B”. No matter how bright you make the remaining lights, the information simply isn’t there.
Hearing aids are about increasing your signal-to-noise ratio so that your brain has a better chance to process what information it has remaining. They can’t completely compensate for the information that is lost. That is why a person with a 70-80 dB hearing loss (such as myself) can hear voices perfectly well with hearing aids, but has trouble actually understanding them.