[I assume police chiefs are vetted and it is made certain that they are sympathetic to the govt.
That must get kind of difficult having to vet all the way down the trough.]
It’s a balancing act. A lot of high level provincial officials are transferred in from other provinces, and it’s not usual for provincial level officials to serve in their home province. The objective was to reduce the likelihood of separatism, something that infected almost all European holdings in the Americas. This isn’t so much a party thing as a remnant from the days when China had de jure emperors rather than just the de facto emperors of today. At the same time, the locals below them not only have local knowledge, they also have local prestige.
In times of trouble, when the ruling family’s fate hung in the balance, it wasn’t uncommon for sub-provincial local officials to decapitate the provincial governors sent from the capital and raise the flag of insurrection. They might be servile in appearance, but many are really just biding their time.