Well Traveller does allow you to whip up a planet on the fly, and that doesn't require being a god. In D&D or most other game systems, there aren't rules to whip up geography on the fly, in cases where it occurs, sure players can get involved with the geography. But in most every other instance, the GM has to make it possible, whereas on-the-fly-geography is not a thing for most games. Again, I've published rules allowing you to create entire star systems and all it's planets - but most games don't have such facility.