I don't think lack of game content is at fault for the low player numbers at this point since it is normal for people to get bored of a game and quit and it would be very counter productive for devs to focus on keeping players locked in the game for months since it is not the only game out there.
This is more of a issue of failure of failing to attract new players. There might be several reasons - no marketing, the 3D in the game looks unappealing for the general population or the existing early game frustration and complexity and not refined basic game mechanics that make them quit on the first day when they try out the game. I think them focusing on refining the mechanics that are critical in the early game would help alot, but most of their dev time they just keep focusing on new things when the old is rarely updated. Not sure how spending months on developing things like AI voice chat tree conversations helps the numbers.