Because when you do, you sign a box of books in about fifteen minutes.
Today was the second day of the Public Library Association's Trade Show and Conference at the Minneapolis Convention Center. It was... ginormous. The Romance Writers of America sponsored a booth there with FREE BOOKS for conference participants, and I just had one of those rare moments in an author's life -- there was a queue around the corner for a copy of my book.
I noticed that the only authors doing give-aways at RWA's booth were local people, and I don't get that. I was ready to fly when I first saw the conference booth mentioned in the RWA Report. A chance to put my book in front of librarians! Heck yeah!
I don't know why any author would object to library sales. Sure, your books get into the hands of readers for free which ostensibly doesn't net you any royalities (although the library does purchase at least one copy of your book). However, my experience as a reader is that "free books" usually translate into eventual sales. I've purchased books from authors that I first discovered on the shelves of the library. It seems to me that given how quickly books disappear from the shelves at the bookstore (you really only have about two weeks before the books get stripped and returned to the publisher), that libraries do authors a great service by providing a place for their books to be "discovered" months and even YEARS after their inital shelf date.
Viva La Library!