Read what I am saying. It is not the book which is the issue, it is the performance. The production of a book is only a symptom. Far too often (the majority of times in my own experience) someone who relies on a book is unable to produce a good performance. Where this is not the case then the use of a prompt doesn't matter (and it is usually only a prompt, rather than reading the words off the page).

I think (atlhough I'm guessing here) that it is mainly about confidence. Someone who lacks the confidence to get through the words may also lack confidence in their performance. A book may help with the first, but without the preparation that learning a song by heart involves they are less likely to overcome the latter.

Performing from memory is hardly niche. It has long been the norm for most genres of popular music. If prompts are used they are usually out of sight, and the singers have the necessary performance skills so they aren't an issue.

Examples from "outside the niche" are only helpful where they are comparable. Church services are clearly not - you arrive at a service not knowing which out of several hundred possible hymns have been chosen, or which version. It is entirely reasonable to use a hymnal. Neither is this a performance. It bears no comparison with a folk club, where a singer will usually perform only two or three songs, of their own choosing,and which they have plenty of time to prepare.

It is certainly true that memory becomes less reliable as you get older. I am in my mid-sixties and notice this myself. However it is also true that memory can be trained, and regular use will help to keep it going. If you are used to memorising songs it becomes easier to learn new ones and to retain the ones you already know. Use it or lose it.