Why did God decide to start something totally different after 2,000 years?
After 2,000 years of utter failure, the human race had rejected God's simple offer of salvation through conscience and blood sacrifice. Despite starting over with Noah, the descendants rebelled again within 200 years at Babel, so God announced He would do something totally different, with Abram appearing at that point.
Les teaches that in the timeline, about halfway between Adam and the cross—2,000 years on each side—Abram appears, later Abraham. Four hundred years before Abraham came the flood, and about halfway between was Babel. Les explains that after 2,000 years of utter failure, God in so many words says He is going to do something totally different. God had given the whole human race the opportunity for salvation: all they had to do was be prompted by conscience that they had sinned and rebelled against the laws of conscience, bring a blood sacrifice, and confess their sin, and God would accept them. It was that simple. But they rejected it totally, until God destroyed the generations with the flood and started over with Noah and his three sons. Then within 200 years their offspring were again in total rebellion and ignorance of God's offer, trying to approach heaven through their own false worship, resulting in the tower of Babel.