The Lord observed the extent of human wickedness on the earth, and he saw that everything they thought or imagined was consistently and totally evil. So the Lord was sorry he had ever made them and put them on the earth. It broke his heart.

Genesis 6:5‭-‬6 NLT

For this he decided not to continue to put up with man since they are but flesh and sinful. He reduced a man's life span not to be beyond 120years Gen 6:3.