Targum Pseudo-Jonathan on (Genesis 6:11) isolates the cause of the Flood. "The earth was corrupted through the inhabitants thereof, who had declined from the ways of righteousness before the Lord; and the earth was filled with rapine."
The Targumist makes the verb active. The earth did not simply become corrupt; it was corrupted by people. Ecology and ethics are fused. What human beings do, the land absorbs. Violence, chamas, rendered here as "rapine", filled the world. Theft, exploitation, the strong devouring the weak. This, more than idolatry, more than even the Watchers, is what finally triggered the Flood.