I think writers attend book festivals for different reasons. When I attend a book festival or a conference of any sort, I want to meet people, talk to experts in the field, and make contacts.
Last year at the Los Angeles Festival of Books, I spoke with authors, publishers, and book sellers. I made an effort to shake hands, introduce myself, and ask them something specific about their product.
One book seller showed me their upcoming publications which might be of interest to my students. A science fiction author shared with me his path to success and offered me a free t-shirt. Of course, some authors are just there to sell their book and, if you’re not buying, they’re not talking. I respect that as well and don’t take their time.
Of course, festivals also have goodies – lots and lots of goodies. I love the swag!