At some point punishments cease to work. Bigger risks of losing everything also mean bigger incentives to retaliate. A poacher threatened with capital punishment isn't going to stop hunting and turn himself in, he will just shoot the police and anyone who is going to report him, because there is nothing left to lose anyway.

Stricter punishment against drugs means dealers choose drugs that are harder to detect. The smaller the quantity of drugs the better. Higher potency is preferred even if wrong dosage sometimes kills the clients and adding foreign substances like brick dust as cutting agent (which then cause the majority of health issues) becomes practically mandatory.