Was Hitler really the worst? Why the ignorance?

For those of you who don’t know, I’ll inform you of some facts relating to my question:

1. MAO ZEDONG- China’s so-called ‘Great Helmsman’ was in fact the greatest mass murderer in history.
China (1949–76) Regime Communist Victims 60 million
Most of his victims were his fellow Chinese, murdered after the communist takeover, starved or killed and tortured in labour camps in the Cultural Revolution of the Sixties.

2. JOSEPH STALIN
Soviet Union (1929–53) Regime Communist Victims 40 million
Stalin imposed a deliberate famine on Ukraine, killed millions of the wealthier peasants as he forced them off their land, and purged his own party, shooting thousands and sending millions more to work as slaves and perish in the Gulag.

3. ADOLF HITLER
Germany (1933–45) Regime Nazi dictatorship Victims 30 million
The horror of Adolf Hitler’s dictatorship lies in the uniqueness of his most notorious crime, the Holocaust, which was carried out under the cover of World War II, a conflict Hitler pursued with the goal of obtaining ‘Lebensraum’. The war ended up costing millions of lives, and his Third Reich in ruins.

My question is quite simple. From the facts, we can see that Hitler was not the worst mass murderer in history. But most people I know and have asked, remain unaware of this fact, and most don’t even know who Mao or Stalin were, or what they did. Hitler is portrayed as the most disgusting human being ever (I’m not saying he’s not disgusting, because he is) but what I’m asking is why people don’t know about the other two disgusting scumbags in history who killed a lot more people and were horrible too. Why is Hitler so much better known? Why does the media/history/literature highlight his crime more than Stalins, or Mao’s?
Again, please don’t take my question the wrong way. What Hitler did was horrendous and I hope he burns in hell (if there is one) along with Stalin and Mao.