cRPG eventually gets boring. Doing the same fucking thing over and over again eventually gets boring. You can try different builds, occasionally play on a new map, or use different gear, but eventually it just gets stale. Eventually you get bored and play the game less frequently. Maybe you leave for good.
There's no marketing, and it's rare that we get new players to replace the ones who inevitably get bored.
The one thing that keeps me playing for longer than an hour at a time is Strategus. I think that Strat, much more so than Battle or Siege, helps foster a community. Normal cRPG gets stale, but Strat's a more dynamic experience imo. Different things obviously attract different people, but Strat does a lot. It creates interpersonal drama, which is fucking entertaining. It gives us some stuff to fight for: virtual castles and villages, nerdy internet prestige, and for those imaginative folks inclined to RP it provides the opportunity to see imagined kingdoms/empires/turf come into conflict. It's certainly not perfect--actually using the Strat interface and dicking around on the map is literally work. It's not fun at all. The fun shit happens during battles, in TS or Ventrilo, and on the forums.
Strat's dead at the moment, though. It has also gotten a bit stale recently, probably because its buggy and kind of doesn't make any sense. Hopefully the devs provide us with a sexy strat soon.
More likely than not they won't and the mod'll die and their new project will flounder and we'll all cry a little bit and maybe poop too and move on with our lives.