Were the daughters of the Godly line so undesirable that the sons of God chose the daughters of Cain over the godly line ? Not that there was anything too godly about any line after the fall
Lamech gives us the reason for this in Genesis chapter 5
Genesis 5:28-29
28 When Lamech had lived 182 years, he had a son. 29 He named him Noah[c] and said, “He will comfort us in the labor and painful toil of our hands caused by the ground the LORD has cursed.”
The faithful people of God began to lose faith and complain about the pain and burden of working a cursed soil. Lamech named his son Noah which means rest as he thought that Noah would bring his people comfort and rest.
What the daughters of men offered the sons of God was Autonomy
Autonomy
1. The right or condition of self-government.
A self-governing country or region.
• Freedom from external control or influence; independence.
Self-government · independence · self-rule · home rule · sovereignty ·
The daughters of men offered the sons of God the autonomy they desired. The sons of God saw the great accomplishments and advances of the sons of men. The sons of men lived a self-governed and independent life aside from God. This enticed the sons of God so they intermarried with the daughters of men and put aside the ways of the Lord and lived their own self determined lives.