Because we are Europeans. We are the world’s Aristocracy. We invented aristocracy. We are also, unfortunately, Christians. Meaning we play ‘extremely forgiving tit for tat’. And so we don’t do that. We civilize people instead. It’s just more profitable.
Look. when the Great Khan was to decimate China, his advisors told him how much money he could make by taxing them rather than just robbing and killing them.
If you’re a westerner, with the only high trust civilization on earth, making customers is simply more profitable than killing them. 3500 years ago the Indo Europeans and conquered pretty much everything from the atlantic to the source of the Yellow River, and from the arctic circle to Egypt, with the Iranians dominating the warm climates and the europeans dominating the cooler climates.
It’s just profitable to rule.
It’s also really hard to profit from rule when almost everyone on earth is dead and the people who are left want to kill you.
The real question is why the west and the russians don’t get together and kill everyone else and just enjoy the rest of history together.