Once you've invested hundreds of hours in creating a coherent universe, your story's grown to around a half-million words and can't be written as anything less than a trilogy.
Short-story writing requires an exquisite sense of balance. Novelists, frankly, can get away with more. A novel can have a dull spot or two, because the reader has made a different commitment.
When I'm not writing or tweaking my computer, I do embroidery. When I'm not plunging into the past, tweaking, or embroidering, I'm reading books about history, computers, or embroidery.