Question: Why did animals have to die in the great flood?

And the story itself is actually borrowed from a Sumerian tale. There was a merchant who protected his livestock and possessions by putting them on his barge when the Euphrates (or Tigris) rivers flooded. As one can obviously see, the parallels between that story (whether totally real or otherwise) are obvious.
The stories of Gilgamesh were passed down through the centuries, along with stories and myths from other sources and eventually morphed into the biblical stories.The Bible ultimately is a compendium of stories from different authors from different sources. Much of its mythos shares parallels with other legends and myths in other religions. Which is understandable. One of the best ways to get followers to your new religion is the familiar. Having stories or myths that share a common theme with ones that those individuals might be familiar with can sway them to your faith. Greek mythology also shares many parallels between Christianity and the Greek pantheon. The concept of an 'underworld' with a malevolent individual watching over the dead. Hades, meet Satan. The idea of a 'son of god'. Perseus, Heracles, meet Jesus of Nazareth.In the end, as Tangle alluded to, how one interprets the meaning is up to them. For those of us that are non-believers, I simply look at these as stories. Either completely made up or derived from actual events and then exaggerated or modified to fit the current narrative.

Who says you have to? For friends and family of mine who I would consider people of faith, for them, god is not invented by humans but the stories surrounding god and the interpretations thereof are invented. The problem arises when religious fundamentalists focus on the literal versus trying to interpret the message. As I mentioned, for those that I know who are also spiritual and believers, focusing the meaning of the story or the message it is attempting to convey is probably the better option.A non-religious example I can provide to convey the concept is the old Star Trek episode called 'Let That Be Your Last Battlefield'. The story revolves around a galactic police officer chasing a fugitive around the galaxy. The two alien individuals have faces that are half-black and half-white. But reversed. Black on the right side for one, white on the right side for the other. And this is the core point of their conflict. In the end, they return to their own planet to realize that the conflict between the two types has resulted in the destruction of their civilization. In the end, they both beam down to the planet and continue to fight, despite realizing that there is nothing left to fight for. Hatred of each other is all they have left.Now what is the ultimate message here? It's an allegory for racism and a warning to us, indicating that hatred between races will lead to our own demise.Star Trek is a fictional show. I don't have to believe that Kirk is flying around in the Enterprise to recognize the core message of the stories.