I thought that putting some writing prompts out there for whoever is reading might get your fingers dancing on the keyboard (or however is the best way for you to write a story). There are already plenty of ideas out there about why these things happen, and you can use the pieces of the stories that came before and make your own story. Your own myth.
Or if nothing on this list floats your boat, think of something in today’s world (natural or man-made) you would like to explain. Go for it. I’d love it if you’d post your myth as a comment below the post. Let your mind flow and fly.