True there is not the largest player base here. But to be honest I've seen games trucking along with a lot less players and activity than there seems to be on this one. And the play style of this game is very niche oriented. It's not a game that every 12 year old on the interwebz will jump into for a few weeks until the next thing comes along.
I'm still a noob myself, but at first glance it just looks like the maps were designed for a player base that just isn't present. Like there are a couple thousand players but the maps were meant for tens of thousands. Other games have ways around this. They expand and collapse the game world according to player volume. They open servers with the same game rules to accomodate additional entries.
It seems that this game is trying to run multiple servers with different rules to accomodate several different preferences in play style. The result is that the naturally small, niche oriented, player base is spread out even further.
Like I said... noob.. could be wrong.