Writing shorts is a different skill from writing novels. I guess reading sjhort stories is also a different skill from reading longer fiction. Reading a novel requires patience, but that is made up for, if the book is good, by immersion in the story. But what if you don't have the time or patience to read a novel at the moment? That's the moment to read a short story.
Only now there's the internet. So all short attention span moments are devoted to email or Twitter or Facebook.
Why do publishers publish anthologies? Or, a question I can answer wtih more assurance: Why does Ghostwoods Books publish anthologies? It's not for the money. It's fo the authors. It's an opportunity for us to meet and work with new authors. It's an opportunity for us to help authors network with other authors. Sometimes new deals or collaborations are struck that way.
It's also an opportunity for us to show the quality and care we put into our books. We have very little control over what gets submitted to us on the novel front. As a small publisher, we're in a kind of Catch 22, where most of the best books are submitted to larger publishers with more immediate money to spend on them, and more clout to get them seen by audiences. We have to work up to that. But in the meantime, we need to publish books to advance.
It's also fun, as an editor, to work on short fiction. There's some art to putting together an anthology, beyond just deciding which stories to take. There's the ordering, to create a certain pacing to the book. In a themed anthology like you want to avoid too many similar stories. But also, you might have a particular slant you want the stories to take.