For reasons unknown to me, fiction publishers seem to believe that Americans only read novels. These publishers, for the most part, shy away from writers who want to concentrate on short stories. One way to get around this as a writer, I think, is to write a passel of short stories with the same main character. Get them published in magazines. Connect them together—you'll know it's really a collection—and tell publishers they're "linked" stories. They'll more than likely publish the collection as a novel anyway, but you'll know the truth.
Not that there's any truth "out there."