“Make yourself an ark…and cover it inside and out with pitch.”
(Here are the first and second parts of the scholion on this verse.)
God could easily have destroyed the entire cosmos and started over. Creating from nothing poses no obstacle to God’s designs. However, He spares those who find favor with him. Even more, He desires that men and women participate in the reconstitution: Noah must save the animals and his family (and we are not told if they have found favor with God as Noah did). God will not work to defeat evil, nor to recreate, without Noah.