China is treating COVID like a crime, not a disease. Very similar to the USA's monumental failure in the "War on Drugs". Although the response in some other countries of outright denial is also just as much a failure, China's response is unique in its failure mode. As citizens will face extreme consequences of being discovered to be sick, or even have someone in their apartment building be sick, by being forced into house arrest, with no guarantee of food or healthcare provided, there is no incentive to declare to authorities that you're sick. Contagious people will go into work, mingle with others, and take no precautions. They may even go out of their way to not self isolate, as doing so would raise red flags. The Chinese government has in effect made its citizens team up with COVID in trying to spread the disease.