Great question. Is there an intergalactic agreement the major players ignore all worlds that do not have warp drive and do not know there is life on other planets? There is a whole galaxy out there trading and fighting each other and each one decides little old Earth etc, despite all its many resources is not worth the time of day? Or maybe they were waiting for us to destroy ourselves so they can land and literally 'inherit the Earth?' Its weird the Andorians had never heard of our solar system, are they that far away, but close enough to Vulcan to stage wars? Maybe each planet stayed in their own backyard, until Humans came along and decided to explore the galaxy?