This article only considered the point of view of the person being unfriended. There are very good reasons to keep unfriending secret on the side of the unfriend-er.

Lack of secrecy will make people less willing to unfriend because of social embarrassment or other reasons. This is a bad thing as people will end up leaking personal info because of awkwardness.

Imagine an old school friend is stalking you. Conventional advice is not to interact with a stalker but to ignore them. Unfriending makes sense but if does/could send a message to the stalker could make a situation worse.