Before speaking about gods and extraterrestrials, we need to understand that whatever the life form is, or how advanced the species are everything in the universe is created and sustained by the same matter and energy, only their proportions and arrangements are different from each other. So the energy which created the humans and other creatures on earth also created some other advanced race of extraterrestrial creatures somewhere in the universe. And as per universe law, the stronger life form always leads and protects the weaker life forms in the universe, just like we humans protecting other life forms by enforcing laws and striking a balance in eco-system on earth. Similarly, the advanced extraterrestrial life or ancient gods have the duty of protecting and leading the new and weaker life forms to strike a balance on earth.
So, if gods or extraterrestrials were technologically more advanced than we humans, and when they had the role of protecting the earth and the life on it, why did they create floods on earth that would wipe the life on earth? When we go through the major religious scriptures of all across the earth, we will come through a story of great flood, where the gods warn a selected human of upcoming flood, and advising humans to build a ship and load it with all living creatures to resume the life cycle on land after floods get cleared. Though the storyline is similar all across, there is never a clear description of the reason behind the creation of floods in none of the religious scriptures. What could have possibly gone wrong? Did aliens attack earth? Or did they bombard earth? If that was the case, they would have not warned us to build ships as a precautionary measure.
But I was able to grasp a story from Hindu mythology that closely resembles the reasons behind the creation of great floods on earth. Just like any other mythology as usual gods fight demons, and in Hindu mythology, gods were named as Devas and Demons were named as Asuras. And as usual, the king of Gods/Devas Devendra/Zeus was fighting an Asura king named Vritra and his large army of Giants/ Daityas in heavens. And the overpowered Devendra/Zeus finally succeeded in defeating Vritra, after the defeat of Asura king the remaining army of asuras consisting of Giants and reptilian beings fled away to planet earth in the fear of getting executed by gods, and took shelter in ocean waters, using ocean waters as cover.
When the night fell, the asura army used darkness as a cover to plunder the earth's resources and also killing humans in the process, and gods failed to trace down the hidden asura army beneath the ocean floors. And to fix the problem the king of gods Devendra/Zeus approached sage Agastya (another celestial being), who could dry oceans. Once the ocean beds were dry without water to cover the god's army was able to trace down the asuras army and kill all of them thus saving the earth from getting destroyed. They then ask Agastya to restore the water but he says he has already digested it, and they should find another way to restore the oceans.

The panicked gods who the whole responsibility of getting back balance on earth, and after a long court session in heaven the gods accepted the plan of bombarding the planet earth with guided asteroids filled with water(Ganga). This also had a downfall of creating huge tides that would drown the planet completely wiping out life on earth. so gods approached selected humans all across the earth to build huge ships and directed them to fill all land-living life forms to resume the evolution back on earth, once the floods get settled. And once the earth was flooded due to the impact of asteroids, the ships filled with different life forms were guided by gods to higher grounds in the hope of restoring balance on earth.
Considering the above story…. Did the Gods hide the real reason for floods from humans? It seems so, because the Devendra/Zeus having decorated the most powerful position of controlling the entire universe, will probably not accept the truth of taking an unsound decision of drying ocean waters of the earth, that could have possibly ended the life on earth. So to cover the truth, many silly stories recorded after the flood, and still, gods hold the sole authority on planet earth after the above incident.