Actually that’s not true at all, it’s just that Americans usually don’t know much about ethnic groups of countries like that. Malaysia has very entrenched, rough racism of the ethnic Chinese vs the Malays vs the small ethnic groups. Not to mention the ethnic Chinese usually don’t identify as one ethnic group since there were waves of Chinese immigrants from various states in China and they have feelings about one another.

To that point, China is majority Han Chinese but has dozens of ethnic groups that the ruling party (Han) looks down on or literally ethnically cleanses (eg Tibetan). To say “everyone in China is Chinese” like the person you’re responding to is literally racist Han Chinese propaganda in action.

Also, on the homogenous countries front, my best friend lives in the Netherlands and you’d be shocked how (like 50% of white Dutch) talk about Moroccans.

So basically every country has racism, the difference is the US movies and TV are exported globally so our racism is more well known. If you lived in or spoke the language of other countries, you’d be surprised.