The 20 - 40 people sticking around will add 20 - 40 people to that radar and at times that 20 - 40 people is almost the entire population of the arena depending on the time of day. It is probably safe to say that the majority of the 20 - 40 people would be on during or around prime time or they would be on prime time for a different, non United States time zone. SO, either way that would be 20 - 40 people back in the meat grinder... .
You have to consider the fact that people are individuals and everyone has their own needs and preferences. People consider 'too few' players to be different values. Some will leave when the number drop below 100, others will stay until numbers drop below 50. That is their personal threshold.
But that is just a root cause, the impact of low numbers is the effect it has on gameplay. With large maps and small numbers gameplay suffers even at 120 players IMO. However if you put 120 players into the old DA it would be chaos. The map size and player numbers combine to make the game fun or not. That is why I talked about population density rather than raw numbers of players.
2 players can have a great game of chess, 3 is a crowd. 2 players cannot play a satisfactory game of football, you need more players to fill the field.
AH needs maps that suit player numbers.
This thread is about why people leave / have left. I am telling you why I no longer play, there is no point debating my reasons, they are what they are and it is actually irrelevant whether you agree with them or not because they are not personal to you, they are personal to me.
I now spend my money in World of Warships because I get fights all the time.