Why is there usually only one candidate on a North Korean election ballot?

In North Korea, the presence of only one candidate on the ballot is a result of the state's highly centralized political structure, which is entirely controlled by the Korean Workers’ Party (KWP).1

Rather than serving as a competitive process to select representatives, elections in North Korea function as a mechanism to register public assent for the policies and programs established by the party. The KWP maintains total authority over the electoral system by drawing up the lists of approved candidates for every constituency. While other nominal political parties and social organizations exist, they serve only to support the KWP, and all political activity must strictly follow the party line. Consequently, the system is designed to ensure that voters confirm the party's preselected choices rather than exercise a choice between competing political platforms.12