By land holdings do you mean land outside of the Japanese Home islands?

Japan had gained much of its empire through aggressive conquest and colonialism, either during the war, or in the few decades preceding the war. Large chunks of China, and the entirety of Korea, were gobbled up by Japan this way. These nations and many others were fighting to regain control of the territory only recently lost to the Japanese. China in particular had been fighting a war to liberate itself from Japan since 1937, four years before America entered the war.

Now I also hope you realize that the US wasn’t fighting a war of conquest, it was fighting mainly to stop the aggressive expansion of Japan (and Germany for that matter). In other words, the US and the rest of the Allied powers were trying to liberate countries conquered by Japan (and Germany), not add these countries to their own empires.

Finally, realize that countries like China were key allies of the US during the war. I hope you see that it wouldn’t make the US look good if they said to countries like China, “We helped you liberate yourself from Japan, but now we’re just going to keep the parts of China that Japan took from you, thanks.” If indeed that would even be possible.