First let me say, I doubt I could write a decent short if my life depended on it. Short stories are a lot more difficult harder to write. Short stories require new plot lines and new characters for every one you write. You also have to condense the story line into a few pages at most, limiting character development, and putting a real strain on the overall story development.
I also think, if I were to become a short story writer, it may make it more difficult to morf back into a novel writer. There's a different dicipline required for each form.
A short story writer gets a reward quickly, when he/she finishes the story, then again if and when the story sells. For a novel writer, that exhiliration of having finished the project is slow in coming and the thrill of a sale even slower. But the rewards of making a sale with a novel are FAR greater than any short story writer can ever hope to achieve, unless he/she has sold a few novels first and the shorts can be combined into an anthology.
Personally, I don't have time to mess with shorts. I have two novels nearing salability. Why should I take the time to write stuff that probably won't get published anyway, and will take away from my work on my novels?
I realize, some people will disagree with me, but that's the way I see it.