you are loud people by default with lots of information; by loud i don’t mean to insult you, i mean you put your point of view whenever needed without any doubt. and so perhaps you don’t need that much of motivation or a blue-button which is asking you to talk.
but not everyone is trained like this. some people, needed to be invited to a discussion. they may have good information or points of views, but they may not have the confidence or they may think of themselves as outsiders.
as a loud person you may not loose a thing if there exist a blue icon which invites you to the discussion, but those who feels less welcome may benefit from this blue icon.