They were incapable of covering their shame. They knew what they'd done was evil, but since they were only "like" God, there was no way for them to go back and replace evil with good.
It shows the extent to which an environment of iniquity can seep into the souls of believers, transforming them from the inside out, so that even when they “flee to the mountains,” like Lot and his girls, they take Sodom with them.
If I am so bound up in the history of the first man, all the way back at the dawn of creation, how can I not also be bound up in the more recent history of my family?