I suspect that’s related to China’s lower levels of individual freedom relative to Japan. Censorship does not fit well with producing powerful and influential cultural exports like manga, anime and video games.

Not being a single-party, notionally communist dictatorship may be helping with the image too? I don't know, spitballing here.

I think the default approach in the West - and that's not a US-specific thing - is to treat exotic faraway lands with a mix of curiosity and awe. But China is a geopolitical rival with a political system that rightly makes many Westerners queasy, so it doesn't benefit from that anymore.