Why would an alien civilization colonize us for anything other than natural resources?

Space is full of mineral resources, going to a random planet with a relatively high gravity well just for some rocks would be counter productive. And an advanced civilization would probably use a lot of automation for resource extraction.

And there are several examples where humans weren't treated well in a resource extraction economy. Sugarcane plantations in the Caribbean were where slaves went to die.

That part is true. But the question is what could the aliens get from us that couldn't be made for cheaper closer to their planet?