And just maybe, they tried it in Kiel as a one off, then when they got a brilliant response decided that the fans would like to hear more of it.

Besides, as a singer, I know that to sing acoustic can sometimes be harder because you have to concentrate more. In a rock song you can just blast it out roughly in tune and it'll sound good. For a more quiet acoustic song, if your voice isn't spot on it's noticed much more, so in some ways acoustic is harder work.