My inclination is that Hitler was the least bad way out of that situation. Give Germany another decade and some other nationalist party would come to power, only this time they’ve got a decade of research behind them and maybe they get the bomb first. Or maybe the leader isn’t a drug-addled former artist who gets his entire staff hooked on uppers and they’re actually effective at defeating their enemies.
So the reason we always seem to have Hitler is because the time cops keep people from killing him because the other timelines are even worse.