Disclaimer: I am not an audiologist, but I am married to one :-).
Because of the way your ears function, the vast majority of people who have hearing impairments have them at specific frequency ranges. Hearing aids do amplify sound somewhat, but they mostly work by pitch shifting voices away from your personal weak spots to wherever your hearing is still strongest. They also do some signal processing to differentiate voice-like noises from other sounds, amplify the voice, and actually mute the non-voice sounds.
For people who have some hearing loss, blanket amplification can be counterproductive and dangerous. Turning up the volume across the board doesn't help at all with differentiating signal from background noise, and can cause what hearing you do have left to degrade much faster than it otherwise might due to the increased stress placed on the ear.
Because of the way your ears function, the vast majority of people who have hearing impairments have them at specific frequency ranges. Hearing aids do amplify sound somewhat, but they mostly work by pitch shifting voices away from your personal weak spots to wherever your hearing is still strongest. They also do some signal processing to differentiate voice-like noises from other sounds, amplify the voice, and actually mute the non-voice sounds.
For people who have some hearing loss, blanket amplification can be counterproductive and dangerous. Turning up the volume across the board doesn't help at all with differentiating signal from background noise, and can cause what hearing you do have left to degrade much faster than it otherwise might due to the increased stress placed on the ear.