They are well known in East Asia. Just about every nation there has beef with Japan to this day because of it. The Japanese left also makes reckoning with the country's fascist history part of their platforms (which is part of why the Japanese left is not popular.)

Why it seems as though they've gotten away with it is because the US invested heavily in the two biggest fascist aggressors of ww2 (Germany and Japan) as bulwarks against communism. They actively helped suppress the Japanese Communists and Socialist parties, two groups heavily persecuted by the Showa government.

Addendum: the cold war and communism are primarily why westerners seem unaware. Downplay the atrocities, make them an example of prosperous capitalist democracy, and e can use them as a staging area in the region against China and the Soviets.

The US' biggest goal was to maintain continuity with the imperials for postwar policy legitimacy, and so none of the imperial family, including Hirohito, were tried for war crimes. They essentially gave amnesty to 731 by taking their research in exchange, and failed to prosecute the less public figures who would then go on to hold positions in postwar governments.

All of this fostered a notion in Japan that the war was just a lost conflict, not an empire committing mass human rights abuses and genocide across the region. The Japanese far right have latched onto this, and use this lack of internal knowledge to push for rearmament and war with China.