Why did the angels do what they did before the flood?

Man has wondered why the angels left their first habitat and took the daughters of men as they may and bore giants in Noah’s day. I believe that they knew the Goodnews of Jesus since the fall of man. In Genesis, they understood that a woman would bring about the Messiah through her seed. Woman does not bear the seed, she carries it. Man gives the seed. The Messiah had to be born through the Spirit of GOD and not of a sinful fallen man via Adam’s seed. Then there was no chance of redemption through His blood. The blood of a Holy Righteous GOD saves. This is why I believe the fallen angels did what they did in Noah’s day. They were trying to recreate what GOD would do through Mary and send us Jesus in the flesh. Their inversion of this only brought about chaos and a world-wide flood. The Gospel was known to Adam and not only that, the Nachash knew.