It’s not about Mars being lower risk but independent risk. Someone could decide to keep copies of important documents in their vacation home not because it’s less likely to have a fire, but because it’s less likely for both houses to have a fire.

I used the wrong word when I said meteor. They’re too small. A comet or asteroid of 100km diameter would raise the temperature of the surface of the Earth by hundreds of degrees and then there’d be decades of darkness. https://www.sciencedirect.com/science/article/pii/S001632872...