Buy in does not work because it is compliance dressed up as an invitation. When we invite someone to do something, we are saying that either a yes or a no response is equally acceptable. When only a yes response is acceptable it is no longer an invitation.
I think that a default setting for a lot of organizations is to gather people for meetings because that is the way we have always done it. It may not be the best way of doing things, but it is a tradition. These traditions can be seen in: weekly, monthly, quarterly or annual meetings. Don’t get me wrong, I believe that it is invaluable to bring people together. I do have a bias about the “why” though.
“If you want to go quickly – go alone. If you want to go far – go together.” African Proverb