![They Live mistake picture](/images/screenshots/66000-66999/66042_sm.jpg)
Revealing mistake: During the big fight scene, you can tell easily that Frank is wearing knee pads (try looking when his pant leg is wet). Construction workers will often wear knee pads for work but most often they wear them on the outside of the pants to save the knees of their pants. (00:58:50)
Answer: As part of the alien takeover, they're suppressing any resistance and discussion of the plot. They know there's a group, led by the preacher, who are onto the conspiracy and that they're somewhere in the camp. They destroy the camp to disburse them and prevent word from getting out.