It's a quality that many writers underdevelop, preferring to focus on characters or plots. Voice is a very scary thing for writers, because it has to do with vision. It's who you are when you express yourself artistically, and it means not copying anybody. Most writers first try to fit into the establishment by living up to the generic idea of a storyist. Lots of the best writing comes from countries where personal expression is restricted, because it forces writers to find different ways to express themselves.
Language is precious and costly.
When I teach, I always teach voice first. It's not just a question of the specific musical notes in a piece, it's about the composer's involvement in the work. When you find your voice, you create the stories only you could have written. I'll never stop writing short stories, but I actually have written a novel, a novel about cyberspace that I was commissioned to write, which I'm revising right now. And I'm working on another one.