I would say that entretenir is a verb with a lot of signification due to its versatility. You can entretenir une conversation just like you can entretenir une salle de bain. A translation of the verb would be like taking care of. An interview is an entretien because you talk to someone: you take care of the conversation. You can also use it like maintenance because you can take care of an object for example.

Hope I helped you!