(5) Hashem saw how great was man's wickedness on earth, and how every plan devised in his heart was nothing but evil all the time. (6) And Hashem regretted that He had made man on earth, and Hashem's heart was saddened. (7) Hashem said, “I will blot out from the earth the men whom I created—men together with beasts, creeping things, and birds of the sky; for I regret that I made them.”

God saw that the time God had allocated to the people to improve their ways had elapsed, but nothing had changed. Nothing but evil all the time - רק רע כל היום, the words every plan (וכל יצר) refer to both man’s urges, the urge to do good (yetzer hatov), and the urge to do evil (yetzer hara). The urge to do good had succumbed to the evil urge, completely...

When God created the human race, God wanted it to be good completely, or at least predominantly. If humankind would turn to be completely evil it could not endure, seeing that God had chosen the good. When God saw that the generation preceding the deluge was thoroughly evil, especially in their interpersonal relations, their use of violence as a legitimate tool to gain their ends, their deeds threatened to undermine the foundations upon which God had built the universe. God, therefore, decided to destroy all those who were evil and to save only the few good ones, so that these survivors could form the nucleus of a better human race after the deluge.

Hashem saw that even reducing their life spans to 120 years did not cause them to repent. This was because their sins were the result of ideology as well as appetite.

One could posit that seeing that God has foreknowledge of all that humans will do, creating them had been an exercise in futility to start with; therefore, why had God bothered? The answer is that everything is under the control of heaven except man’s decision to either live in awe of the Creator or to defy the Creator. Seeing that God had decided to create a creature equipped with free will, God had simultaneously abrogated the right to interfere.

And now, O Israel, what does Hashem your God ask of you? Only this: to revere Hashem your God, to walk only in God's paths, to love God, and to serve Hashem your God with all your heart and soul.

See, I set before you this day life and prosperity, death and adversity.

ויתעצב אל לבו And it grieved him on his heart — He mourned at the failure of His handiwork. Similarly ‘The king grieved (נעצב) for his son”.

The following extract from the Midrash Rabbah I am writing in order that you may know how to refute the arguments of certain heretics: A gentile once asked Rabbi Yehoshua ben Korcha, saying to him, “Do you not admit that Hashem, knows what is to happen in the future?” He replied, “Yes.” The gentile retorted, “But is it not written ‘and He was grieved in His heart’?” He answered: “Have you ever had a son born to you?” The reply was “Yes.” He asked (the gentile): “And what did you do?” He replied: “I rejoiced and I made others rejoice also.” The Rabbi asked him: “But did you not know that he must die?” The gentile replied: “At the time of joy, let there be joy, at the time of mourning let there be mourning”.

The Rabbi said: “Such, too, is the way of Hashem: although it was clear to Him that in the end men would sin and would be destroyed, He did not refrain from creating them for the sake of the righteous men who were to issue from them”,

'וינחם ה, the expression, וינחם, “He was sorry, He regretted,” has been chosen by the Torah in order for human beings to have at least an inkling of what God’s feelings were when He faced destroying His handiwork. Clearly, such emotions as “regret” are not part of God’s vocabulary. We have it on the authority Samuel I 15 29 that human feelings such as regret, frustration, are not feelings which can be attributed To Him.

Rabbi Yehuda says, "[God said] that I regret that I created man below [on earth] since if I had created him above [in heaven] he would not have rebelled against Me."

Rabbi Neḥemia says, "[God said] that I am consoled that I created man below [on earth] since if I had created him above [in heaven], then just as he incited the lower worlds against Me, so too he would incite the upper worlds against Me."

Rabbi Aivu says "[God said] that I regret that I created the evil inclination, since if I had not created it, he would not have rebelled against Me."

Rabbi Levi says "[God said] that I am consoled that I made man and placed him on the earth [where he eventually dies]."

(14) And Hashem renounced the punishment planned for God’s people.