This doesn't happen when a singer is hunched over their song book struggling with the words.

Who suggested that? You can use a written text while performing with as much spontaneity as anybody doing without, there is no need whatever to "hunch". Performing that way is a skill that needs to be learned - but anybody who wants to can learn it.

Somebody not only performing from paper, but performing something he'd written himself from paper:

Allen Ginsberg

How many folkies have ever got paying audiences as big as he did?