I don't know, I just have this idea that we aren't actually on the top of the food chain so to speak. Maybe it's farming for genetic diversity. Or maybe you start civilizations to get them to birth bespoke AI personalities, or some other wacky idea.
Yea, I feel like Aliens is not so far out of a possibility, and the theories are fun to play with... yet something grounds me and says there just are (and have been) some really smart people out there.