What is the significance of Genesis 6:5–6?

Seeing the wickedness of the whole human race which preceded the great flood, the Bible says, “The Lord was sorry that he made humankind on the earth, and it grieved him to his heart.”

If everything about world history was exhaustively settled and known by God as such before he created the world, God had to have known with absolute certainty that humanity would come to this sorry state, at just this time, before he created them. How then could he truly regret his decision to create them? Conversely, if we accept that Scripture is speaking plainly here and God’s regret was real (the fact that he destroyed the human race and started over with Noah suggests this, does it not?) then it seems more reasonable to believe that until that point in time, God didn’t know with certainty that humanity would grieve him the way it did.