For a start, war crimes should be prosecuted much more comprehensively than today. I think most criminals do make some kind of risk/reward calculation. Even the nazis did that when they dug up mass graves and tried to hide the evidence.
Just like nothing really happened to Russia for invading and still supporting Ukrainian border conflict. Israel's atrocities vs gaza strip and pushing out their border. US committed war crimes, white phosphorous drone strikes in random countries.
As you said only weak countries are targeted by the justice.