People think the existence of emperor (thousand years long) itself wasn't the root cause (or at least think it's better than changing everything), unlike Hitler.
I'd argue it's a different story looking from inside Japan. A sizeable part of the population aren't questioning going to war in the first place, and only put the blame on the military for having attacked the US. Basically they blame the country for having been too greedy, and see the current jp/usa relationship in that light ("why do we need to import so much US beef ?" "Because we lost" is something you'd hear with only half sarcasm)
That is to me a fundamental problem that was one of the root cause of the war, and stil causes issues to this day. The lasting conclusion should have been "don't invade your neighboors", not "don't attack the US".
To be clear, I don't think Japan will ever invade Korea or China again, but their diplomatic relations are still somewhere stuck in that age on both side. And if Japan had a venue where the international community wouldn't beat the shit out of them, they'd still go for full domination.
Japan took Korea from China, hence it being a Sino-Japanese war. Japan took control of Manchuria form Russia. They took Indochina from the French.
I think it is fair to say that Japan was following the dominant playbook of the era. They were literally taking colonies held by other western powers, as the western powers often did.
I think that is a pretty high expectation to hold for any former or current empire. Outside of Germany, I can't think of one who drew that lasting conclusion. I don't the English, French, Dutch, or Spanish spend a lot of time regretting empire. The US only makes small noise about the conquest of the native Americans. Literally nobody cares about the taking of Florida, Cuba, Puerto Rico, and the Philippines from Spain, or Texas and California from Mexico.
Given this context, it it pretty easy to take "don't attack the USA and loose" as the lesson. The success of the USA is global example of what happens when you don't lose existential wars.
Before attacking the US, they had Korea and Manchury invaded, and Russia in check. The extent of their dominance relative to their country size was really impressive, and they went for the US because they needed to feel unstoppable.
Then of coure, they were stopped. But none of the base roots of the war were removed, the emperor was allowed to stay, they made token trial of random generals who committed atrocities.
But no one was allowed to officialy question:
- the US carpet bombing entire Tokyo (for comparison we questionned Germany carpet bombing EU towns) and dropping the bombs on civilians
- the Japan's spiritual leader and basic phyolosophy. Really, imagine Hitler being excused as a mere puppet and staying as a philosophical leader after the war.
In that respect, The compromise the US took looks to me like the critical difference from Germany, where they could move on and jointly create the EU. Instead, Japan and Korea are still barking at each other over the war almost a century later.