Consult Genesis 6:5-7
"5 The Lord saw that the wickedness of man was great in the earth, and that every intention of the thoughts of his heart was only evil continually. 6 And the Lord regretted that he had made man on the earth, and it grieved him to his heart. 7 So the Lord said, I will blot out man whom I have created from the face of the land, man and animals and creeping things and birds of the heavens, for I am sorry that I have made them."
God is patient, and administers justice in His own time.
Romans 9:22-24
"What if God, although willing to demonstrate His wrath and to make His power known, endured with much patience vessels of wrath prepared for destruction? And He did so to make known the riches of His glory upon vessels of mercy, which He prepared beforehand for glory, even us, whom He also called, not from among Jews only, but also from among Gentiles."
FReegards!
There are gradients of evil. The kind of evil exhibited pre-Flood is obviously different from that exhibited by modern man is my point.
Many Biblical scholars (Michael Heiser being the one who stands out) point back to Genesis 6 as the source of that particular evil.
BTW, there is more to the event--Babel--that just what is presented in the Hebrew Bible. There are many ancient literary/mythic sources from which to triangulate this story. The Sumerian/Mesopotamian sources shed light on this event--albeit from an entirely different POV.