Let's first figure out why democracy rises in the first place: It's because some events, the Industrial Revolution for example, created a bunch of wealthy middle classes, who then sort of became the driving force of their country and start to demanding for rights.
Middle class exists for very long time before official democratization, and I don't think they just sit there and waiting for rights raining on them, rather, I believe they're constantly demanding for more rights. It's just the society takes time to change.
In China, something like Industrial Revolution never actually happened because of invasion, war and stupid government decisions. As result, we also don't have middle class people until after the Economic Reform[0] which is very recent compare to other countries.