It's not though. The question makes the assumption that he would have been handed over for the Nuremberg trials.
But the Soviets were fucking ruthless against Nazi Germany. They were REALLY driven by hatred for them. If a Nazi soldier surrendered to Russians, a summary bullet to the head was often the more merciful outcome.
And it was the Russians that would have found Hitler first, so it's far more likely that they would:
execute him on-the-spot
torture him until death
have their own trial for him in Russia before torture/execution.