Chicken Soup for the Soul books are just one example of a collection, or anthology. Even authors who have published ‘stand-alone’ books often write for anthologies, too.
Why?
For authors, publishing in an anthology offers a diverse and larger audience than having all their stories in one book.
And~
An anthology, where several authors write on the same theme, offers readers a variety of perspectives and styles.
For myself, I wrote in two short story collections last year: Desert Tapestry and Christmas Tapestry. Then just last week, I published in a Novella collection, Journeys of Forgiveness.
As we are beginning our sales and marketing, I see that splitting the costs four ways, instead of bearing the costs alone, is another great reason to write in collections—at least part of the time.