> For comparsion, in the US as of 2023, nearly 48 million inhabitants (14.3% of total) are foreign-born (https://en.wikipedia.org/wiki/Immigration_to_the_United_Stat...). Or the Netherlands, 4.4 million of its ~18 million inhabitants are from abroad (https://en.wikipedia.org/wiki/Demographics_of_the_Netherland...).

The relative population size of those countries likely plays a role there. Split China into 4 countries, each with a population about equal to that of the USA, and I bet that number for China goes up significantly. Split it into 75 countries each the size of the Netherlands, and it would go up even further (some people moving home within Beijing would emigrate)