Hello, half-baked space person here. Of all the speculative answers on why another civilization would contact us: The flip side is our own (to extend the metaphor) child-like curiosity of the cosmos around us. Are we truly alone? What could we learn from other life (technologically, biologically)? Where are they at in their civilization's development? Is there evidence/ hope for us to come to a place of global unity or overcome existential troubles like climate change without great loss [actually the first link covers this too]? Edit: So both points I meant to link were from the same conversation. The link above would start at what I sought to answer. The start of Sagan's dialogue with Carson on the search for terrestrial life on that date: It touches most of the conversations and some jokes along this thread. Worth a fun, informative listen.What made this optimism nevertheless terrifying was the unknown of what the adults of the cosmos would be like. Would they be peaceful? Would they be so advanced that they would treat us as we treat a fruit fly or a rat, or a lab mouse, or even Laika the space dog? Would they treat us as food, the way we treat cows and pigs? Would they carry with them genocidal new diseases the way Europeans did to the Americas? Would they be the disease? Would they demolish the Earth to make way for a hyperspace bypass?
Clifford Simak's "Big Front Yard" of 1959 presupposes that in a universe of abundance, the only reasons to interact with other species are cultural. After all, if it's natural resources you need there are plenty of planets unbeloved by angry natives who don't want their water taken. The example from "big front yard" involves small mouse-like aliens who take a bunch of spare parts from a Yankee trader and pay him back by turning a black'n'white TV in for repair to color. He then discovers their "stargate" for lack of a better term and wanders out into the plains of interstellar commerce where he discovers that while humans have not invented antigravity, apparently we're the first culture to come up with coating things in different-colored pigments for purely aesthetic purposes. There's a later story from the '80s, the title, author and gist of which I cannot recall, but it was an archetypal "the aliens are among us" story with the argument that duh they're here for the culture. The only thing I do remember was the extremely poignant example of rabbits: the alien in the story explained that any number of races could look at a rabbit and produce any number of reproductions but to date, only one culture has come up with a "wascally wabbit." If you think back through the history of human exploration, minerals provide a short-term gain, biological specimens a slightly longer gain, but what we've gotten from exploration, over the long term, has been cultural exchange. It's undoubtedly anthropocentric to assume the same about an encounter with other species but really, the one thing we're likely to have that's unique to us is our culture.