It is obvious that the author doesn’t care what Enoch did. Enoch was the only one right in an era of general corruption (see Gen 5:22). It is only said that Cain begat Enoch and built a city bearing the son’s name (Gen 4:17). It is said the children he begot, but not that he behaved well unlike Cain or Lamech. Indeed, as we have observed, Cain appears as a very different character from the one who had killed Abel and had been cursed by God to wander the earth. On the contrary, he seems to have a permanent home, where he sets up a family. Cain is also the progenitor of a generation. He even built a city, the exact opposite of his wandering condition.
The intention of the author is also confirmed by the verse 19. The verse speaks about Lamech whose conduct represents a further step forward in the degeneration of humanity. It is said that he had two wives: Adah and Zilla. The names of these two women effectively exemplify a very confused society, where good and evil overlap, a chaotic society. Adah is an Hebrew name that means to shine while Tsillah means shade. Even the fact that the text says Lamech took two wives is quite indicative of the violence and arrogance with which a man takes not one but two women. The hebrew verb laqach is simply followed by nashim – i.e. women. There is a certain vein of brutality in what Lamech does. He takes two women as they were objects.
In short, the author seems interested in describing the growing violence that dominates the mythical and archetypal society that will be destroyed by the flood waters.