Physics

I'm biased as a biologist, but I don't think extraterrestrials will reach out to humanity until we've solved both global peace and biological immortality (the second being much easier and closer than scifi makes it seem and likely a prerequisite for the first). Until we have a population that's basically capable of responsibly managing themselves, I think humanity looks like infants or maybe teens throwing tantrums. Unstable, unreliable, and in need of the time to work itself out.

That's assuming of-course that they're near by in the first place, which is unknown.