The back story says that they have terraforming technology. If that is the case, why didn't they head to a Goldilocks planet that has no sentient life and take over it. Humans have nukes and certainly will not take kindly to aliens arriving with planet terraforming technology.
They're refugees from a destroyed star system. It stands to reason that they didn't have the luxury to find an ideal world, but had to settle for what they could reach.