Rich Food
Aliens make contact with earth. They communicate via radio before arrival. They try and find out about our society and who's in charge, who's important, who isn't. They finally believe they have an understanding of how things work, and they ask if they are correct that the "best" people are the rich ones and the "worst" are the poor. The powers that be agree that if you had to choose, then yes, obviously rich people are better than poor. The aliens show up and take the rich folks away. The rest of us are left alone. We aren't worth transporting because there isn't enough profit in us, because the beings they sell to prefer rich foods.