Very simple explanation: it's impossible, unless the West can mow the rogue regimes left, and right, and is ready for a war with a nuclear power to do that.
> When China was very poor, it didn't really matter, or perhaps the assumption was that China would liberalise more quickly than it has.
Expecting a communist party to "liberalise" is effectively to expect it to kick itself out of power. The moment they loose power, their people will murder them. And if people wouldn't, then it would be their internal factions who will strangle each other without an iron handed big boss at the top maintaining internal order.
There is no way out for them. Their only way to avoid being torn apart alive is to stay in power, and their only way to stay in power is to exert, push, and expand it.
For them, to stop repressions, means to let their enemies to take the proverbial rifle from which barrel's the power grows, and to seal their fate, essentially to voluntarily chose death.
Any totalitarian system has an expiration date for this very reason.
In case of China, what that means is an instant gulag, or worse for 5 political dynasties:
1. Few remnants of Mao, and his wife's reign, and their confidants for, well, everything.
2. Deng Xiaoping's era communist billionaires, who will have to return millions they stole from the state in eighties.
3. Shanghai people, and Jiang, who will have to at least surrender their posts, and titles which they bought, and sold illegally, and all privileges coming with them.
4. Hu's clique, whose members will have to surrender their businesses, and stocks which they got through connections
5. And finally, Xi, and his friends, who managed to make a bigger mess in their 8 years in power, than the three previous dynasties combined.
Put it simply, do you expect a thief to voluntarily give a gun to the person whom he just robbed? An expectation that the West can share the planet with rogue regimes, is an expectation that a kleptomaniac, and a really rich person can live under the same roof. Even if the later can keep the former compliant under a gunpoint for some time, eventually the former succumbs to his urges, and the later has to shoot.