I think it's a form of relaxation. I have always created worlds, story backgrounds, invented places. Using the AD&D formula means I don't have to concern myself as much with the mechanics of things. It's like a processing program that allows the creative juices to flow. Creating both stimulates and rests my mind. It gives me an escape from daily pressures and an outlet for things that my RL work doesn't give me much room for.
Do I expect to ever have someone play in these worlds? Probably not. It would be nice, but it's been a looong time since I had a group of friends to play with -- or the energy to get together and do so. stryck keeps talking about creating an on-line website where we could play games. That might be nice. She remembers me as a DM; I think she and some other old-timers might like to play a game of my making.
But, really? Just a harmless daydream, more like.
* Old saying that arose from a wargame-playing group I was in nearly thirty years ago (c. 1979). It quickly spread to other games and groups I was associated with. Lots of my family and friends probably say it when they play, without knowing its origin.