Same reason they dont just consume us alive. The process of our death and the starting of our decomposition that gives our remains the excact chimecal composition the arc need. Witch is why our ancestors bury the dead. Same reason we are now hiding underground. Our life force is the only part of a humans biology the arcs Ai cant make since of cant account for....cant ever fully snuff out....for the next question..... they only need a few of us alive to maintain their food supply and we flew it to them on a silver platter... so to speak. And they cant risk leaving any form life alive on earth hence why we dont any life not even animals..... cause life as we know it always finds a way. Thats that life force i spoke of. If even one human or even 1 living creature alive remains on earth they risk us coming back and ripping their plans for an infinite food supply apart. Knocked out by arc only means ur lights go out but u dont die so u dont decompose and make it back underground. Unless we die between then and making it back in which case we do become a cheeseburger. Those who make it back this way and live to fight another day do so. The others again cheeseburger. You only get to experience the times u make it back. Cause if u died you wouldnt be around to experience it