For context - Trotsky's own position on the Sino-Japanese War was far more reasonable:
We do not and never have put all wars on the same plane. Marx and Engels supported the revolutionary struggle of the Irish against Great Britain, of the Poles against the tsar, even though in these two nationalist wars the leaders were, for the most part, members of the bourgeoisie and even at times of the feudal aristocracy...In the Far East we have a classic example. China is a semicolonial country which Japan is transforming, under our very eyes, into a colonial country. Japan's struggle is imperialist and reactionary. China's struggle is emancipatory and progressive...
But Chiang Kai-shek? We need have no illusions about Chiang Kai-shek, his party, or the whole ruling class of China, just as Marx and Engels had no illusions about the ruling classes of Ireland and Poland. Chiang Kai-shek is the executioner of the Chinese workers and peasants. But today he is forced, despite himself, to struggle against Japan for the remainder of the independence of China. Tomorrow he may again betray. It is possible. It is probable. It is even inevitable. But today he is struggling...
But can Chiang Kai-shek assure the victory? I do not believe so. It is he, however, who began the war and who today directs it. To be able to replace him it is necessary to gain decisive influence among the proletariat and in the army, and to do this it is necessary not to remain suspended in the air but to place oneself in the midst of the struggle. We must win influence and prestige in the military struggle against the foreign invasion and in the political struggle against the weaknesses, the deficiencies, and the internal betrayal."
(Leon Trotsky, On the Sino-Japanese War, 1937)
Note the conclusion of "We must win influence and prestige in the military struggle against the foreign invasion and the political struggle against the weaknesses, the deficiencies, and the internal betrayal" - even if skeptical in the KMT being a reliable ally, completely the opposite of "never collaborating with the bourgeois KMT government", and definitely not advocating for taking up arms against the KMT yet.
So, why did the Chinese Trotskyists have a different, incorrect position? Because they were already getting violently purged for years with the help of the KMT out of reasons initially completely unrelated to the Sino-Japanese war. They were already a fringe, beheaded tendency in China, their leaders imprisoned or dead, which is why their positions deformed in this way, and not because they were dirty Trots who just want defeat for all communism. But they sure did make a convenient bogeyman nevertheless.
Because unlike the dumb trots, MLs and MLMs definitely always have the correct party line on everything, especially the less members they have and the more generally obscure they are, am I right?
In fact, this is why you can just choose any ML or MLM party you want, no matter how small, and engage with just that one party's line, because they are actually all equally correct! For example, let's say the Italian PMLI, who... support sending weapons to Ukraine?
Uh-oh, not a good look for the Stalinists!