Detta förklarades i en io9 intervju med direktören Neill Blomkamp. Kort sagt är räkorna en hive art. När deras ledare dog, blev de rudslösa (och inte lite dumma och lättsamma). I avsaknad av kommandoinmatning och inse att tillgångarna var korta, navigerade fartyget dem automatiskt till närmaste beboeliga planet för att tillåta dem att lossa och utföra reparationer. Tyvärr stötte de på oss.
Det var som om det var så lång tid för en potentiell ny ledare (Christopher) att fullt ut mogna och börja göra intelligenta planer på hivens vägnar:
What is your own back story for these aliens? What's their home planet like? Why did the end up on Earth?
The other thing is that the ship was meant to clip together with other ships. So there's, like, vast amounts of resources that they're bringing to the parent planet. And the ship, when the army generals or the queen of that particular ship died off by some sort of virus or bacteria that they picked up on some other planet, that killed them off. And it didn't effect these sort of resilient, hardy sort of drone workers. Then the technology is usually the thing that they relied on to save them, but in this case it sort of screwed them because it brought them to a planet that kind of treated them pretty badly, but it was the ship that realized that, unless it gets to a life sustaining planet everything is going to die, which is a cool idea. So the ship just auto-pilots to the closest one in the Goldilocks band, and it's our planet and then pulls up and hits the brakes.
Where does this leave Christopher Johnson [an abnormally smart prawn who sparks a bit of a revolution... Not to give too much away]?
I think it's taken 20 years. I think because there is a subconscious hive mind happening, really what they should do is lay one egg that has a different embryo in it that grows into a Queen or being someone that dictates direction. But I think in the interim, because they may have done that, there may be an egg out there with that, but as that being is growing, I just like the idea that he may have been a lot more directionless in the beginning. But the hive structure of their society may just pick one or two that starts to become the leader. Like the overall structure of his brain may change because the hive may want that to happen. So he starts having a direction and a goal. Which is an interesting idea and it's just enough to kick start them to be able to get to the ship to get back.