In the context of the story, destruction is vastly cheaper than protection. Imagine the same system except everyone has instant access to a perfectly guided bun

In the context of the story, destruction is vastly cheaper than protection. Imagine the same system except everyone has instant access to a perfectly guided bunker buster. It doesn't matter if you're better armed. The bunker buster will bust your bunker. And while you need to discover to bust bunkers likewise you only have to be discovered to have your bunker busted. So the farmers die instantly even if they find others like them to band together. The darkness of the forest is key too. I imagine the effect is similar to the effect air power had on castles.