Why did authoritarian governments keep the concept of politicial parties around, even when the ruling party was the only one?

by ilovethosedogs

For example, in Nazi Germany and Communist countries, when other parties were banned, why was the concept of the central party still important? Wouldn't it have been the goal to get rid of the concept of political parties in order to legitimize that party's ideology as natural and the only game in town?

Like when the Nazis banned the opposition, why did the Nazi Party continue to function and have a concept of membership distinct from the notion of German citizenship, instead of being integrated into the government?

Or in the Soviet Union or China or North Korea, where the leader was/is the Chairman of the Communist Party; why even bother having a "party" when the state and government are literally custom built around that party's ideology? Why does this seem to be so common?

The Korean Worker's Party (WPK) and its opposition parties in North Korea (DPRK) serves a number of functions. What those functions are boils down to the illusion of choice and a guise of legitimacy.

Admittance into the WPK is (one of) the only viable means of upwards class mobility in the country. Not only have you suppressed all other ideologies, but you're also awarding those who tout the party ideology and serve their Dear Leader. It's essentially a requirement to have served for a number of years in the Korean People's Army (KPA) in order to gain admittance into the WPK, further exposing any individual who wants to survive in North Korean society to indoctrination.
While it's incredibly apparent to you and me that the Democratic People's Republic of Korea is anything but, the permittance of political parties brings an air of legitimacy to the government, however thinly veiled. Kim Jong-un was elected by an overwhelming majority of North Koreans, but the elections are usually single-candidate races, and any candidates coming from opposition political parties must be first selected by the WPK. Moreover, to vote for a candidate other than the one in the WPK requires the crossing out of the Dear Leader's name (it's a criminal offense to physically, verbally, or otherwise tarnish members of the Kim Family's image or name), and any non-WPK votes must be placed in a separate booth while the rest of your village watches you. They also monitor who doesn't show up, one of the many tactics to find or capture defectors. Having "elections" gives legitimacy and further surveillance over the population.
Were a DPRK citizen to join one of the two opposition parties, they would undoubtedly be increasingly monitored and labeled as subversive. It's a lot easier to put the "bad eggs" on a list when they willingly sign themselves up. Those labelled too subversive in the group would be immediately swept away. Regardless, opposition parties are effectively rubber stamps for the WPK, as they are legally required to accept the ruling role of the WPK.

While I can't speak about similar governments to the same level, the main facet of sustaining authoritarian governments or cults of personalities is control: They keep us safe with these rules, they feed and clothe us in exchange for our love, the best life we've ever lived was serving them.

"Without you, there would be no us! Without you, there would be no motherland!"

Edit: a word