I have been using delay and reverberation since the middle 1960s. I use them to make what is almost inaudible to the ear, audible. I do not use them to play loudly but to make the higher harmonics heard.
Rock musicians, and a vast array of popular-music musicians, due to their wealth, acquired through the mass of their notoriety, are able to be listened to and heard and thus are able to effect change on an international level.