Why has the black market continued to thrive in china

Probably because it’s so hard to purchase items due to the harsh laws, so to get the things they want they just purchase them illegally

An informal structure in a bureaucracy would be something like so-called "office politics". where there's a formal structure set up for the organization, but then an informal subculture as well that has a way of organizing the bureaucracy further. this can be positive because it sets up an added degree of organization, albeit informal, within the bureaucracy.