they already work almost for free, since all the money goes to the publisher and retailer.
out of $20 book, the authors earn about $1 - $1.5, for e-books its about $1.7 - $2
The value from book sales goes to retailer and publisher: two large corporations, and in case of amazon - a single big corporation
so please cry me a river about amazon's lost profits earned at the back of the book authors