“Since the dawn of man” is really not that long,
As every galaxy was formed in less time than it takes to sing this song.
— ‘Big Bang Theory’ theme
Why do it at all?
Starting with a creation myth is by no stretch the only (or even the best) way to start word-building. It is the toppiest of top-down design design approaches. However, I think it has some advantages.
First, I think its a good way to set the tone and major themes of a campaign. If your major conflicts are between good and evil, you can set them up from the very beginning. If you want a more nuanced political situation, you can bake it in to the universe.
Second, it helps justify the choices you’ve made in world-building. If magic works a certain way, it can be reflected in the very makeup of the universe. Want dwarves to hate elves? Have the gods give the surface to the elves and depths below to the dwarves and let conflict ensue. Also, its a great backdrop element to drop in plot clues and campaign goals. What if the garden of Eden was real, and the tree of life still bore fruit? Wouldn’t intrepid adventurers want to take a bite?
So call it cleverness or conceit, but that is where I am starting.
To recap, we are building a fantasy campaign for The Fantasy Trip rules. It is a roughly bronze/iron age environment with no connection to our historical Earth. Our civilizations are relatively young, as the world has recently faced some kind of cataclysm destroying all the previous societies and structures (but leaving behind tantalizing treasures and profound mysteries).