That's very interesting and surprising but logical,
audio books can serve as a very
relaxing source of entertainment after a hard days work heading back home on the train or during unscheduled recess in the morning at school when the library hasnt opened yet, it's also a good way of winding down when the children have been put to bed and you just need an hour by yourself in the couch without a noisy tv
with advertisements interrupting the welcome calm of evening.