> Every couple of months one of his friends will get banned for no reason

Are they seeing the exact same screen as the one in the original post? There are two separate systems at play, each individual server has moderation by those who host the server (wherein they can ban anyone for any reason) and there is now a global moderation system introduced very recently, which is run by paid moderators hired by Microsoft.

You said "every couple of months" but this system did not exist before last month, at least on the Java edition of the game.