Why do flight attendants close the full overhead bins when people are still boarding? Later boarding passengers will inevitably open all the closed bins as they gamely search for a place for their bag. I think the flight attendants close them because they have already convinced themselves there is no more room and it is time to go. They may be right. The problem is that the passenger with a bag to stow is not convinced.
Leaders need to be sure people understand their thinking and what facts are supporting decisions to move. People will get on board, but the process will be more effective if people are seeing the same things that the leader is seeing.