Books have been around for quite some time. The major change isn't that the marginal cost is now zero. The incentive and techincal ability to use copyrighted works without a license has been present for a long time. The difference is the decentralization. In the past, if you printed a batch of unlicensed books, it was very easy to shut you down or sue you. Now, anyone can make the copy and it's not viable to go after them all.