Here's why:
* Poaching is against the law: The Capitol controls all resources and food production. Poaching would be a direct challenge to their authority and could lead to harsh punishments.
* Black Market is actively suppressed: The Capitol maintains a strict control over the flow of goods and information. The black market would be seen as a threat to their economic and social order.
* Enforcement is a key element: The Capitol has a strong security force (Peacekeepers) and informants throughout the districts to enforce its laws and eliminate any opposition.
However, there are some nuances:
* Survival necessitates it: In the districts, particularly the poorer ones, poverty and hunger force people to break the law to survive. This is shown with characters like Gale, who hunts illegally to provide for his family.
* The Capitol's hypocrisy: The Capitol is shown to be corrupt and hypocritical, often engaging in activities like illegal trading and exploiting the districts' resources for their own gain. This suggests a double standard and highlights the unfairness of the system.
Ultimately, the Hunger Games depicts a world where the law is enforced by the Capitol to maintain its power, but the harsh reality of survival often forces people to break those laws. The black market and poaching exist as a consequence of the Capitol's oppressive system, not because of its protection.