That was what I was thinking, the moderators are not under any obligation to provide explanations when either temporarily or permanently banning a member. I think I have only seen one instance (not the one you referred to in the Croatian board) where a moderator might have made a comment but they do not give a running commentary.
Rightly or otherwise, moderators are not under any obligation to elaborate to others when banning but they do informed the recipient of the reason along with the length of time. I do think there have been and will be cases where members will question a ban but if moderators are not under obligation it will take a huge effort to try to get them to comment.
What happens when a user receive a ban for plagiarism, do the moderators comment on every single temporary or permanent ban with a justification or explanation?
They rarely do that, but there have been cases where some of the more active mods have posted explaining why the person was banned. In some cases they would even quote the post/posts that got them banned. There really is no way to tell why they decide to comment in some threads and remain quiet in others. When a local Croatian board member got banned, we tried to lift his ban for almost 2 years. In all that time, I don't remember the admins commenting or saying anything in the thread until the ban was lifted one day and the only post was from the mod who unbanned the user. He simply said that the user is now unbanned and end of story. I think that was hilariousandco.