North Korea makes decisions that constantly harms it's people. Conducting nuclear test after nuclear test, for what? To say you have one? To have another toy to saber rattle with? All while preaching that it exists in a sheltered paradise. All while its people starve.
Giving them aid even though they defy what pretty much everyone in the world asks them to do (even China is getting towards their wits end), only allows them to defy even more. To abuse their people even more. Not aiding them at least gives their people a chance to see what is really going on. Sadly that means some people may starve, and I'd hate to see that happen, but honestly, what else do you do?