Probably showing 3/4 would have been potentially confusing, so it was just easier to put 3 on one side and 4 on the other. They had the space, and it reduces the chances of players using the wrong one.
OK. I understand that. Thanks for your thoughts. However the importance of the probability of bad cards could imply that there is no reason to adapt the meter for 2 or 5 players... It is possible that the dynamics is different with these (extreme) numbers of players (?). I still have a doubt but I need more experience with the game to know what is best.