Why are there so many stories about rainbows?
No one truly has any idea why rainbows are so enigmatic, mysterious or magical. Way back then in the days before modern science rainbows would be viewed as magical occurrences and it wouldn't have seemed like there was any pattern to them. The Norse thought of them as something that happened when their gods wanted to get somewhere (not Thor however because he was way too heavy). Now they're seen as symbolic (must resist) and are an icon of the LGBT community.
That's Polychrome, daughter of the Rainbow in the Oz books. Just another example of the rainbow's irresistible pull. I will now leave you with a YouTube video.