I have had two people ask me this question in the last week, "What are you training for?"
While I do jump into some events now and then, my stock answer is, "Life. It requires tremendous endurance."
Really, I maintain a certain level of fitness so I can do the fun things I like to do, pretty much at the drop of a hat, and enjoy myself. I also believe that keeping a certain level of fitness gives me the quality of life now, and is an investment in my future quality of life.
When an event sounds fun I might rearrange my "training" to better suit a particular event. That written, I'm really training for life.