The Basic Plot Hole

Overall, this was a decent attempt to provide entertainment. Yes, it was low budget and silly, but so is most everything made for TV. However, there was one basic flaw I cannot overlook - if space bacteria crave metal, why are they chasing humans for the minerals in our blood after they were put in a junk yard? The junk yard is their motherload, and they wouldn't leave until they consumed all metal within it. Only then would they would begin their search. . .for more metal! So if they stopped cars they would go after the car, not its driver. Humans would only become prey when they run out of metal.