The reason no one would accept the 999999/1 split is because it is a terrible choice from an evolutionary perspective. You're getting pretty much nothing while

The reason no one would accept the 999999/1 split is because it is a terrible choice from an evolutionary perspective. You're getting pretty much nothing while your genetic competitor gets a huge advantage. This is not rational. Natural selection would cause the genome of people who accept this split to be less likely to survive. Accepting only even splits helps select for cooperation. If your neighbors are more likely to work with, share, and help you and your children, your DNA will be more likely to survive.