The US maintains its sanctions against the DPRK (and Cuba, and Iran, etc.) by having established a credible threat of violence against anyone, including civilians, that might attempt to ignore or circumvent them. Those sanctions also directly target civilians as well because they include banking, which has the practical effect of blocking things like medical supplies even if such goods are explicitly permitted in the sanction orders. The Yemenis are doing a comparatively better job of not targeting civilians in spite of the less sophisticated means at their disposal.