@basedbagel For the same reason backstabbing does 2x damage in RPGs, it's much easier to win when your opponent has their guard down.

But it's because betrayal is so effective, that collectivists haven't dominated the world and individualism still stands a chance. The biggest perk of being alone, is that you don't have to worry about the people around you.
And the greatest folly of empires, is internal conflict.