So why are these aliens coming to Earth in the first place?
Jonathan Liebesman explains: "Earth is 70 percent water. The aliens in our movie use water for many different things, so they are here for those natural resources."
Or as Winston Churchill would have put it:
People are accustomed to their birth culture, I guess. There is no way around it: people know what they know. One grows up absorbing the values and behaviors of one's own culture and develops patterns of thought reflecting the culture as normal.
This is, no doubt, one of the things that make it difficult for scriptwriters to imagine behaviors of entities from a different culture from the perspective of what a different culture could possibly be like rather than from their own.