Because he knows that, if he doesn't keep the citizenry scared and angry, he's getting voted out and going to prison.
That's all there really is to it. He's killed hundreds of thousands, made the world a less safe place, triggered resurgent antisemtisim and put a target on the backs of the collective Jewish diaspora just to save his craven political skin from prison.
I hope there's a hell, and that he and Henry Kissinger end up sharing spots by the lake of fire.