When theatre patrons can’t make out the dialogue they stop going. There’s no point. But a hearing loop can bring them back. A hearing loop works with a special switch on a hearing aid. It sends the sound from the speaker directly to the aid. Yes, there are other types of hearing augmentation. But who wants to go to ask for a special device to hang round your neck? Older people generally shun assistive technology because of the perceived stigma. Hearing loops are far more discrete. See this video of a case study that surprised a theatre manager.
There are several types of hearing augmentation systems, but hearing loops are preferred by users. Other systems don’t cut out background noise or require a special device to be worn by users. English subtitling is sometimes used for operas so that patrons can follow the story. Captioning is a similar system and could be applied to live performances as well.