Comment by Arn_Thor

The takeover was deftly executed, with the kind of patience only a government not concerned with elections can exhibit. While local elections came and went, and the opposition parties valiantly fought in the public sphere, the institutional takeover was slow but steady. That is the only way the pro-China powers in government were able to outlast and suppress the protests in 2019. The government faced unprecedented public opposition, but enough people at all levels of government feared for their livelihoods that neither the bureaucracy nor the police reached a critial mass of sympathizers.

Another crucial factor that's part of the CCP's victory in HK is that China inherited a police force essentially structured as a colonial occupying force. Police staff get benefits that include segregated housing (such as the West Kowoon Disciplined Services Quarters), which maintains morale in the ranks and allows those so inclined to live quite separately from the rest of the populace.