How is there enough meat in a short story to make a make movie out of it? Apparently it can be done. Examples: The Shawshank Redemption based on the short story, Rita Hayworth and Shawshank Redemption by Stephen King. Alright, not a great example as it was a novella so somewhat longer than the average short story.
Then there is Brokeback Mountain, based on the short story of the same name by Annie Proulx.
There are probably a lot more out there but I don't have time to look for them.
It's just interesting what screenwriters can do with something fairly small. I haven't actually read the above mentioned short stories but it is going to be a mission of mine to actually check them out.