Experience Tumblr like never before
... but the reality is (in the Spy x Family universe) is that the war didn't just affect Twilight and Yor, it affected a whole lot of other people. The war stole a lot from them; livelihood, wealth, families, and the possibility for a future happiness.
And because Twilight and Yor hated so much what happened to them, they don't want another person to go through what they did. Preserving the peaceful lives of other people is what motivates them to be the best person in their respective jobs.