It's entirely a wrong idea to think political system should evolve this quick.
China's political system inherits form 2k+ years of feudalism tradition. The system is largely static, with unsubstantial decorative changes here and there. And eventually it collapsed in the face of Western invasion. This humiliation period spans almost last a century, and is defined as the "Century of humiliation" [1].
The unique timing, and combination of various rather lucky events gave birth to the CCP.
CCP took an approach that is seemingly unconventional, while fundamentally is just another round of emperor-style dynasty evolution. Mao was effectively an emperor, who by chance or intentionally managed not to have his own heir. He also did exactly what has been done before in the history, where new emperor killed almost all of the people who helped him ascend the throne, because these powerful people would become a threat to his heir (be it his own blood line or someone else).
Nonetheless, in less than a few decades, China went through feudalism to communism. This level of change is unprecedented and would likely be impossible in the future.
After culture revolution and the open border policy, China's political landscape also changed a lot. Not in the same scale of the CCP and PRC's establishment, but still quite spectacular compared to any other countries in the world.
1. China's economic growth allows more free expression of opinions through various of channels. In a nutshell, any democracy is a compromise between rational economy groups with matching political power. China's economic growth allows many individual to gain the power necessary to influence the political system. Is this system better or worse than western democratic system? Hard to say, but it's different.
2. Chinese people learnt to respect the bottom line of the CCP, but find constructive ways to express their dissent over government or political polices. People can easily overthrown low-&middle-ranked government officials by showing hard evidence of corruptness over various non-official channels. Such channels, like Weibo, Wechat groups, are regulated, but is not shutdown. The rate is maintained in a way that CCP's bottom line is always maintained, and without touch that, things can be liberal.
3. Chinese people have learnt the truth of propaganda both internally and internationally. I would rate Chinese people the most independent-minded group of citizens in the world. Chinese people are incredible at recognizing propaganda and superficial arguments that bear limited practicality.
CCP also was changed substantially. It now has over 80MM members, and vast majority of them are from all sorts of social background that has nothing to do with elite or any form of privileged groups. However, the bad thing is that CCP now becomes a bed for marrying the powerful and the rich. The rich ones join the rank of power list of CCP.
The whole thing is moving towards the direction as most Western countries, i.e., the political system becoming a tool for the rich and powerful to maintain their status.
In conclusion: > The thought was that China's steady economic liberalization would inevitably lead to political liberalization
China's political system has changed drastically over the same period, much more than any other country in the world.
In the foreseeable future, China will not move in the direction desired by the western countries. Thousands of years of political wisdom have taught Chinese people to balance between different ideologies and maintain the peaceful life of themselves. The only possibility of such change is that a foreign power invaded China and forced her reform in a fashion that is different than what Chinese people collectively desire.
Extreme conditions will not be tolerated, and irresponsible social revolution will not be welcome. Chinese people will be following their own wisdom in finding the true liberation of the nation, most likely through the continuous economic growth.
That's like the relationship between typical Chinese parents and their offsprings. Are the parents abusive compared to western counterparts? Yes. Does the offsprings get what they need to grow and become independent? Yes. Then why destroy such relationship? The answer, of course, is not to do such a thing.