When a group has no effective model for working together, people believe meetings are places where everyone talks about whatever shiny conversational objects appear, whether from participants or the person supposed to be leading the meeting. This ensures nothing will be achieved, which is sometimes the agenda of the leader and others in the group who seek to avoid all forms of responsibility taking and sharing.
Having agendas makes no difference in a shiny object culture. Within the scope of any topic, the group can free-associate itself into endless and fruitless discussion and debate on whatever shiny objects appear to attract people's attention.
The antidote is an effective model for the process. These can be and often are a logical yet flexible series of questions that can move the group from ambiguity to action.