Regardless of whether the accusations about defectors being coerced to make North Korea sound worse are true, honestly this just sounds like an obvious consequence.
If you isolate a country economically by cutting off all legal ways for it to trade with the international community, it will have to rely on illegal ways.
Generalized trade sanctions have time and again proven to be ineffective because they are so indiscriminate. They're meant to work as a deterrent, not a punishment. But the deterrent works with the threat of disrupting the economy, which only works short-term as the existing supply chains come to a halt and businesses panic. If you sit the sanctions out long enough, the economy will have already collapsed and will rebuild itself under the new restrictions. Once the economy has adapted, the sanctions are no longer a deterrent, they're just how things are, and the promise of conditionally lifting the sanctions feels like a trap because it would require changes to the economy that would again make it vulnerable to those sanctions if they were reinstated.