because they are unsustainable and can only be maintained for some time with careful management.
Is this a fact --- or a hope?
China is a different culture and is carving it's own path --- one that doesn't exactly match any that came before.
The West expected that it would change China. What is actually happening is China is changing the West.
For example, trade with the USA is now controlled by one person. It's hard to get much more authoritarian and anti-capitalistic than this.