I think sometimes a story is just a story until it's done. That has certainly happened to me. I make a sim, they have something they want to achieve, or better yet, some sort of struggle to overcome, then once they succeed (find the perfect match, raise x number of kids and send them off to college, get rich, build their dream home...) I feel done. It's like writing a book, sooner or later the story ends. Maybe you just prefer short stories over long novels? Nothing wrong with that.
I do agree with keeping old sims in game when you create new ones. There is a satisfaction to seeing the accomplished sims you've created continue on with their lives. If you leave neighborhood stories on, they'll progress and maybe then you'll see a reason to revisit them after a while.
