Of Adam and Eve’s children, only three are biblically remembered: their first child Cain, who was exiled for murdering their second child Abel; then followed by their third child Seth. Adam and Eve had other sons and daughters after Seth. Genesis chronicles the lineage of Seth, which includes Noah, and curiously, Genesis includes Cain’s lineage as well.
All known history had filtered through Noah at the floods end. The stories in Genesis were memorized, not written. Noah might just as well have deemed Cain’s lineage unnecessary, as was the case for other children of Adam and Eve. Had Noah excluded Cain from his teachings, Cain’s descendants would be unknown. One should assume that Noah had reason to protect with care the memory of Cain and Cain’s descendants.
For Noah, there was one notable reason to save the memory of Cain’s lineage. Noah received significant help from Cain’s descendants in the construction of his ship. They were likely responsible for food stores and supplies, and for technology involved in the ship’s construction. In a sense, Noah owed Cain’s descendants for his shipbuilding success and for his life- the redemption of Cain perhaps.