It's about the same reason why Vulcans got attached to us. They're a curious species. They didn't necessarily expect gain other than to satisfy their curiosity. They'd probably have respected lab rats about as much as they respected humans.

But I generally disagree with the OP above you. As far as observations go, the universe seems like a rather lonely place. I don't think a lot of science fiction is far off. Either from a civilisation looking to make friends or slaves. Both are sensible plots. The uselessness of humanity portrayed in that post seems incorrect and highly pessimistic. Evidence of that is easy enough to find just by looking at the rest of our solar system. We may be far from perfect but for something like us and all other life on earth to be born out of such chaos seems to beat the odds and so far we have no evidence of otherwise.

With that said, I don't think humans will ever reach a state of perfection. I don't think our universe allows that. Maybe outside our universe.