All three of these Prime Minister pages appear to be "unofficial" meaning that they are not managed by a Project, but rather by three individual WikiTree members.
Members are permitted to create profiles on any topic they wish. There is no rule that says they can't duplicate topics already covered, and unlike profile pages, there is nothing that says they must merge their profiles if they don't want to. It might seem redundant, but people have their own rationales for what they choose to do.