Instead of God drowning people and making them suffer could he have not just stricken them dead instantly?

I believe in God but sometimes the bible stories really don't make sense to me. If god is all knowing then why did he make people and then he found out they were evil and felt the need to destroy them in the great flood and start over... and now their is evil in the world again. Didn't he know that it wouldn't work the second time as well.