The flood (keep in mind this is mythology from the early chapters of Genesis) came because fallen angels mated with human females to create a race of giants called Nephilim. God saw how violent they were being so he decided to start over with a new, purely human race. YHWH would have been more of an abusive daddy if he had let that crap continue! Who wants to live in a world full of Andre the Giants clubbing people to death like they're baby seals?!