One thing to consider is that number doesn't indicate the precise number of players at the table at any one time. It just means that number of players participate in the campaign. For example, when I ran a West Marches game years ago we had 25 players at any one point participating, but usually only 6-7 showed up for an actual game session. Then, the next game had 6-7 players too, but it might be a few different players swapped out or something.