China has developed its rare earth resources and those of other nations while the west has slept. If you read the article linked you would understand this.

'“It’s just the way China does things. They have tended to build more capacity whether it’s in aluminum, or cement, or nickel,” said William Adams, head of base metals research for Fastmarkets. Chinese companies “all gun for market share, and the consequence for that is you get oversupply.” Western officials, too, are sounding the alarm. In response to a question last month about China’s dominance in nickel, Canadian Deputy Prime Minister Chrystia Freeland said the market had been flooded, making businesses in free-market democracies uneconomic. '

Its not that the Chinese innately have hugely more rare earth reserves than others but rather that they have deliberately and strategically developed their capacity while the west slumbered on its delusional US exceptionalism.

China has played the west at its own game of capitalism and imperialism- and won.